The water clock that Abbasid Caliph Harun al-Rashid (d. 809 CE), gifted to Charlemagne, the Holy Roman Emperor (d. 814 CE) is investigated. Origins and transfer of the clock technology is reviewed. The water clock mechanism is envisaged based on various descriptions of water clocks including those by the Royal Frankish Annals, Imam Abu Hamid Al-Ghazali, Voltaire, Edward J. Wood and the clocks of Baghdad (such as that of the Mustanṣiriya School), the clocks of Al-Andalus (Such as those by Al-Muradi and Al-Zarqali), the clocks of Tlemcen (Algeria), the clocks of Fes (Morocco) and the clocks of Ridwan al-Saati and Al-Jazari. The most likely mechanism of the clock is constructed using modern engineering drawing from which a 3D animation is produced.
At the peak of the Abbasid Caliphate’s geographical and political power it was presided over by the Caliph Harūn al-Rashīd (d. 809), perhaps one of the most famous of all Caliphs, resided in Baghdad. He was an exact contemporary of the most celebrated monarch, the Holy Roman Emperor and King of the Franks, Charlemagne (d. 814), who resided in the city of Aachen, in the far west of modern-day Germany. The two monarchs were in diplomatic contact and exchanged delegations and gifts. Harun al-Rashid sent a delegation from Baghdad to the court of Charlemagne in Aachen bearing the gift of a water clock.
The water clock was not the only gift that Charlemagne received from Harun al-Rashid during his long reign. He received a whole host of other lavish gifts including a live white African elephant, a golden tray and a pitcher set, perfumes, a set of chessmen, bolts of fine cloth, a large tent and a richly woven robe embroidered with the Arabic phrase “There is no god but God”. These gifts were in return to those that Charlemagne sent previously to Harun al-Rashid. Charlemagne gifts included rolls of royal red fabrics, which were highly valued in Baghdad. Although Charlemagne’s clock did not survive the passage of time, some of the gifts he received from Harun al-Rashid are extant and can be found today in Aachen, Saint-Denis in France, and as far away as Durham in England.
The white elephant was probably transported by ship from North Africa since the overland route through Anatolia and the Balkans was far too unsafe. The second, and final, Abbasid delegation to visit Charlemagne was the one that brought with them the brass water clock. It is said that amongst the delegation were two representatives of Thomas, the Patriarch of Jerusalem, and a Christian monk by the name of Felix. They reached Aachen in the summer of 807 CE and the Arab official in charge of the delegation gave a demonstration of how the water clock worked and how it was to be maintained. In all likelihood, the clock was carried to Aachen in its component parts and assembled there since such a delicate piece of machinery would most probably have been damaged en-route. The third and final delegation from Aachen to Baghdad arrived at its destination in 809 CE, but Harun al-Rashid had passed away a few weeks before its arrival.
It is claimed that the delegation was made up of two counts, named Lantfried and Sigismund, and a Jewish merchant named Isaac, who was to serve as their interpreter.
The exchange of gifts was a vital part of medieval diplomacy, but it was not simply an exercise in courtesy and diplomatic niceties. A gift from one king to another could be a great civilisational ‘power-play’, so to speak. This was the great significance of the water clock as a gift. The water clock, a complex piece of precision engineering, conveyed to Charlemagne an idea of the richness of the civilisation from where Harun al-Rashid came. It was a powerful statement that science in the Muslim world, Baghdad in particular, was at the cutting-edge of innovation. The significance of this message would not have been lost on Charlemagne who surrounded himself with scholars.
In terms of solid results, the alliance of Harun al-Rashid and Charlemagne did not achieve more than a loose understanding on trade and communications, but such was the fascination in Europe with Harun al-Rashid that even the elephant that he gifted Charlemagne— named Abul Abbas—had become a household name in France and Germany. This was so much so that the historian of the Royal Frankish Annals, normally concerned only with kings and wars and eclipses, was sufficiently moved by the elephant’s death to break into his narrative in 811 and add “the elephant which Harun, King of the Saracens sent, suddenly died”.
These sorts of time-keeping devices were unknown in 8th century Europe and their arrival in Charlemagne’s court fascinated those who saw the device. The story of this episode and its technical sophistication were carried through the centuries, Voltaire (1694-1778) describing this clock, said:
“Harun al-Rashid’s striking clock gift to Charlemagne was regarded as a wonder. Regarding cognitive philosophy, sound philosophy, physics, astronomy and principles of medicine, how could they have been known [to Muslims], these had only just been known to us?”
Unfortunately, this clock did not survive to the modern period. Its appearance, however, was noted in the Royal Frankish Annals, a chronicle, written in Latin by various Frankish churchmen, which recorded noteworthy current events from the years 741 to 829 CE. The following is a translated extract from the Royal Frankish Annals for the year 807 CE:
“Radbert, the emperor’s emissary, died on his way back from the East. The envoy of the king of Persia by the name of Abdallah came to the emperor with monks from Jerusalem, who formed an embassy from the patriarch Thomas. Their names were George and Felix. This George is the abbot of Mount Olivet, a native German and called, by his real name, Egilbald. They came to the emperor and delivered presents, which the king of Persia sent to him, that is, a tent and curtains for the canopy of different colours and of unbelievable size and beauty. They were all made of the best linen, the curtains as well as the strings, and dyed in different colours. The presents of the Persian king consisted besides of many precious silken robes, of perfumes, ointments, and balsam; also of a brass clock, a marvellous mechanical contraption, in which the course of the twelve hours moved according to a water clock, with as many brazen little balls, which fall down on the hour and through their fall made a cymbal ring underneath. On this clock there were also twelve horsemen who at the end of each hour stepped out of twelve windows, closing the previously open windows by their movements. There were many other things on this clock which are too numerous to describe now”.
It is worth noting that a book written in London in 1866 by Edward J. Wood, entitled ‘Curiosities of Clocks and Watches from the Earliest Times’, which was an expansive survey of the development of clocks in Christian Europe since the Medieval period, noting Harun al-Rashid’s gift of a clock to Charlemagne, said:
“In the year 807, the King of Persia, Haroun al-Raschid, sent… to the Emperor Charlemagne a timepiece, which represented the first rudiments of a time-clock. According to Abbot Eginhart, who was an eyewitness of it, twelve figures of horsemen when the twelve hours were completed issued out of twelve windows in this horologue, which until then stood open, and returning, again shut the windows after them as they marched back. This appears only to have been a water clock, curiously constructed of brass. The hours were noted by the striking of a cymbal, and the striking of the hours was managed by the fall of twelve brass balls on a bell or bells placed beneath them. It is recorded that this clock had many other curious mechanisms and was regarded as a great novelty in Europe… [John] Giffford (1758 – 6 March 1818) in his, ‘History of France’, thus describes Charlemagne’s clock: “but what particularly attracted the attention of the curious, was a clock worked by water. The dial was composed of twelve small doors, which represented the division of the hours; each door opened at the hour it was intended to represent, and out of it came the same number of little balls, which fell one by one, at equal distances of time, on a brass drum. It might be told by the eye what hour it was by the number of doors that were open; and by the ear, by the number of balls that fell. When it was twelve o’clock twelve horsemen in miniature issued at the same time and, marching round the dial, shut all of the doors.”
Wood’s book chronologically examines over 600 individual clocks and watches. The ‘King of Persia’s timepiece’, as it is called, is placed right at the beginning of his work in the section dealing with the very earliest clocks. It is the first clock mentioned by name and discussed at length following a short general discussion on sundials and rudimentary Roman, Greek and Ancient Egyptian water clocks. Wood’s placing of ‘The King of Persia’s timepiece’ as the first clock in his chronological study indicates that he saw it a seminal clock that marked the transition of timepieces from crude to advanced devices. In the mind of this 19th-century European, who almost exclusively discusses Christian-European produced clocks in his work, the water clock of Harun al-Rashid was the first step on the road to modern clocks and watches.
In order to appreciate the significance of Harun al-Rashid’s clock, it necessary to examine the state of the art and background of such clocks.
The essential prime mover and controller of a typical water clock is the movement of the surface of water contained in a vessel that has a small orifice. The most common vessel is the outflow clepsydra, which is a vessel that has a hole near its base allowing water to leak out, hence changing the water level. The outflow clepsydra was probably transmitted from its place of origin in the Fertile Crescent to other areas during the 1st millennium BCE.
Besides the outflow clepsydra, there is another simple ancient clepsydra that Eastern Arabs knew as a ṭarjahār. It is a submersible bowl, with a hole in its base, placed on the surface of a body of water. The time taken for it to gradually sink to the bottom is used as a timer for reference. Its most common use was to fix the periods for the allocation of irrigation water for individual farmers. In India, it is called Ghatika-yantra. According to the Greek historian Callisthenes (ca. 360-328 BCE), the Persians were using such a device, but calling it fenjān, in the early 4th century BCE to ensure an exact and fair distribution of water from qanats to farmers. Fenjāns were also found in public places in pre-Islamic Persia where they were used as crude clocks to record the elapsing of hours.
An important development in water clock technology was the introduction of the inflow clepsydra, which probably came into use in Egypt shortly after the outflow type, arrived there from the Fertile Crescent.
There is an interesting legend that was common amongst Ottoman clock-makers: The famous traveler Evliya Celebi reports that some clock-makers he saw considered Prophet Joseph (Yousef) as the father of clocks. They believe that he made a device to tell him time whilst he was in the darkness of prison. Considering the prison condition, it might have been a sand clepsydra (perhaps the origin of the hourglass we use in modern kitchens). There seems to be no primary source corroborating this story.
According to the Roman engineer Vitruvius (d. 70 BCE), from whose book De Architectura we have the earliest and most complete information from the classical West, this technology was invented around 250 BCE by the Hellenic Greek inventor and mathematician Ctesibius (d. 222 BCE), who lived in Ptolemaic Egypt in Alexandria. He built an inflow clepsydra in the city that used the motion of a rising float to engage gears and cogwheels that brought about the movement of various automata like falling metal balls and sounding trumpets. The hours were marked on a pillar and indicated with a pointer.
Archimedes of Syracuse, who was a contemporary of Ctesibius, also made great progress in the field of clepsydra technology. He was the first scholar in the West to take the basic water clock model into a piece of sophisticated machinery that released metal balls to strike bells and gongs and worked automata like opening doors and windows and moving figurines of people and animals. Archimedes’ work in this field is likely to have been preserved in an Arabic treatise on the design and manufacture of water clocks known as the ‘Pseudo-Archimedes Treatise.’ Later, in the 1st century CE, Heron of Alexandria (d. 70 CE) wrote a work (now lost) on the construction of water clocks and the theory behind their functioning. There seemed to be a monumental water clock in the main square of the ancient city of Gaza, Palestine. It was described by the Byzantine historian Procopius (d. 537 CE). It included various automata such as birds discharging marbles, the sound of trumpets and cymbals, and 12 doors that opened in succession once every hour. It would be a historical challenge to investigate whether these features found their way to the clocks of Harun al-Rashid, Ridwan al-Sa’ati and Al-Jazari?
Around 30 CE, Chinese philosopher Huan Tan (d. 30 CE) notes the effects of temperature and humidity on the rate at which water flows, thus affecting the accuracy of clepsydrae. The Chinese polymath of the Han dynasty period, Zhang Heng (d. 139 CE), invented the first hydraulic-powered armillary sphere, which was powered by a waterwheel and incorporated an inflow clepsydra, the latter of which he improved by adding a compensating tank between the reservoir and the inflow vessel.
Around 450 CE, Steelyard clepsydras are mentioned as being in widespread use in China, with the implication that they had long been in use. In 610 CE, Chinese engineers of the Sui dynasty period, Geng Xun and Yuwen Kai, improved the clepsydra by providing a steelyard balance that allowed seasonal adjustment in the pressure head of the compensating tank, which could then control the rate of flow for different lengths of day and night. The Chinese astronomer and engineer Yi Xing (d. 727CE), along with his associate Liang Lingzan (a government official), invented a striking water clock featuring an escapement mechanism and a water-powered rotating armillary sphere – a device that shows the apparent positions of stars in the sky.
On the top right (Figure 4) is the pictorial reconstruction of the astronomical clock-tower built by Su Sung and his collaborators at K’ai-feng in Honan province, then the capital of the empire, in 1090.CE. (Original drawing by John Christiansen).
There seems to be a gap in history about Chinese clock technology coinciding with a period of the rapid development of clock technology during the Abbasids in the Muslim world.
The re-emergence of Chinese water clock technology is noticed when one of the most famous Chinese water clocks is constructed by Su Sung in 1094 CE. Standing at around 30 feet tall (not counting the 10-foot observation platform) this clock was an engineering marvel. The clockwork, driven by a water wheel, and fully enclosed within the tower, rotated an armillary sphere on the top platform and a celestial globe in the upper storey. The shaft of the tower contained five floors. The floors had doors that would open, and mechanical puppets would come out giving notice meanwhile of the passing hours and quarters by signals of sight and sound. The puppets would also play the drums and stringed instruments as well as ring gongs and bells.
It ran until 1126 CE when it was dismantled and moved to Peking. It only ran for a few more years after that. The clock was eventually destroyed. The original Su Sung sketch, of the clock, is depicted in Needham.
We know that Muslims had a longstanding trade with China which must have facilitated exchanges of expertise and know-how in both directions.
We know Muslims had first arrived in China at the dawn of Islam in 628 or 651 CE. The Australian leading historian D Leslie accepts 651.
Leslie, on the other hand, dismisses many of the contacts prior to Islam, but also holds that:
It is, in fact, only with Islamic and Arab dominance that trade expanded enormously, especially by sea, and a real Chinese knowledge of the Near East developed. Chinese sources do in fact make clear that Islam was known to the Chinese as early as the 7th or 8th century, not long after the death of Muhammad in 632 C.E.
Between 650-1 and 798, the Muslims sent thirty-nine formal embassies to China. Gibb makes the crucial remark that ‘Official Chinese records document these embassies, though the Arabic historical tradition makes little mention of them. This makes the Chinese sources that much more valuable.’ For the extensive book by S E Al-Djazairi on “Islam in China”.
An interesting case of technology transfer is that of papermaking. Eleven hundred years ago Muslims were manufacturing paper in Baghdad after the capture of Chinese prisoners in the battle of Talas in 751. Paper-making spread from Samarkand to Baghdad by 794 and was quickly reﬁned and transformed into mass production by the mills of Baghdad and spread westward to Damascus, Tiberias, and Syrian Tripoli. The Chinese used the bark of the mulberry, for raw material. The Muslims used hemp whose ﬁber length and strength meant it produced high-quality paper. Today, hemp paper is considered renewable and environmentally friendly; it also costs less than half as much to process as wood-based paper. They also introduced linen from linen rags which were broken up, soaked in water, fermented, then boiled and cleared of alkaline residue and dirt and beaten to a pulp by a trip hammer, a method pioneered by Muslims; though it was the Chinese who first invented the trip hammer back in the Han dynasty, being used initially for paper-making and later on in sugar and iron production as well as for milling flour. For more on the story of paper-making in the Muslim world, see the 4th edition of 1001inventions book.
Thus, it seems inconceivable that there were no interchangeable influences between China and the Muslim world at that time.
Could the situation with the European renaissance had been replicated with China, in that Muslims saved and built upon the knowledge they received from them and then transmitted reformed versions back to China as they did with Europe?
There does not seem to be a clear evidence of the background of Haun al-Rashid’s clock, but we know that time telling technology was not uncommon to the area.
The common use of water clocks at the time of Harun Al-Rashid is evidenced in the writings of the poet, social commentator, and zoologist Al-Jahiz (776 – 868). He would have been at the age of 31 and in Baghdad at the time of Harun al-Rashid’s gift to Charlemagne. He mentioned in his Kitab al-Haywan (‘The Book of Animals’) that:
‘Our caliphs and scholars use astrolabes by day and bankamat (water clocks) by night for the telling of the time.’
Abu Ali al-Hasan Ibn al-Haytham (965-1039 CE) was born in Basra. He died 20 years before Al-Ghazali was born. From the lists of his works quoted by Ibn abi Usaybi’a and Ibn al-Qifti, and based on other modern studies, it seems that Ibn al-Haytham authored only one text on mechanical engineering, the Maqala fi ‘amal al-Binkam, a short unedited treatise extant in two copies preserved in the Süleymaniye Library in Istanbul. It describes an original water clock. A full description based on this treatise is published by Al-Hassani, In this text, Ibn al-Haytham discusses in great detail the construction of a water clock, therefore, making it a work of rare importance in the history of clock technology. He himself described this water clock as being unique, saying that there was “none like it before.” His intention in constructing the water clock was born out of his frustration at the inaccuracy of previous clocks and his desire to create a genuinely accurate timepiece. It seems, however, that Al-Ghazali must have not been aware of it as he described a clock controlled by an outflow clepsydra, whilst that of Ibn al-Haytham was controlled by an inflow clepsydra. Ibn al-Haytham thrived in Basra before his migration to Egypt. People of Basra, a seaport, must have been aware of the inflow clepsydra used in Persia (named as Fenjan or Tarjahar) and in India (named as Ghatika Yantra).
In the year 1233 CE the Mustanṣiriyya madrasa opened in Baghdad. It was named after the Abbasid Caliph al-Mustansir bi’illah Abi Ja’afar Mansur (d. 1242), son of the previous Abbasid Caliph al-Zahir bi’amr Illah. The first madrasa in Baghdad, the famous Nizamiyya, had opened nearly 200 years earlier in the year 1065 with the generous sponsorship of the great Seljuk wazir Niẓām al-Mulk (d. 1092). Soon afterwards madrasas sprang up all over Baghdad and spread to most of the great cities of the Muslim world, including Damascus, Cairo, Isfahan and Herat. Madrasas were purpose-built, endowed institutions of higher learning that incorporated teaching spaces, libraries, dormitories, prayer hall and kitchens into one building complex. The Mustansiriyya of Baghdad was a seminal institution in that it was probably the first madrasa to broaden the scope of its curriculum to include mathematics, engineering, astronomy, medicine and veterinary medicine, amongst many others. Miraculously the Mustanṣiriyya escaped the horrendous sacking of Baghdad in 1258 by the Mongol army of Hulagu. Ibn Baṭṭuṭa described it when he visited the city in the year 1327 as being frequented by students.
In the year 1235, a building was completed on a portico opposite the Mustansiriyya, which functioned as an open-air clinic staffed by a doctor and his assistants, who would sit behind a stone counter at the front of the portico, facing the street. A clock was built into this street-side clinic so that it faced the entrance of the madrasa. It was designed and built by a Baghdadi engineer by the name of Ali Ibn Tha’lab (d. 1269 approx.), who is described as being famous for his expertise in astronomy and horology. His son, Ahmad, became a renowned scholar of Islamic law according to the Hanafi School. As a result, we came to know about Ali as he appears in an entry about his son in Al-Fawā’id al-bahiyya fī tarājim al-ḥanafiyya, a biographical dictionary of Hanafi jurists by the Indian scholar Muhammed Abd al-Hayy al-Lucknowi. Ali Ibn Tha’lab’s clock was in the tradition of the clocks of Damascus, with a row of opening and closing doors to tell the time during the day, bird figurines dropping metal balls into vessels to announce the elapsing of an hour during the day. At night, there was a function that used lights to tell the time at night, and a function to mirror the movements of the heavenly bodies also. The Mustanṣiriyya water clock was described in some detail by the Baghdadi historian Ibn al-Futī in his al-Hawādith al-jāmi’a li-‘l-tajārub al-nāfi’a fi al-mi’a al-sābi’a. This book deals with the events of the 7th Hijri century in which he lived. As a Baghdad native and contemporary of the clock it is safe to assume that the description below is either his eyewitness account or one that he heard first hand from others:
“On the outside wall of this counter was a circle on which there was a depiction of the heavens, and on it were many finely decorated bronze arches housing finely decorated doors. Within the circle were two model falcons, made of gold, each inside a golden bowl. Two bronze ball bearings were positioned behind each falcon so that they were not visible to the observer. At the moment of the elapsing of an hour, the mouth of each falcon opened and out fell the ball bearings. Each time a ball bearing fell, one of the doors inside the arches opened. The doors were golden, but they now became silver (i.e. the golden door was replaced by a silver one). When the ball bearings fall into the bowls below they then run on back to their original positions. Then golden planets ascend into the azure sky within this depiction of the heavens simultaneously with the rising of the real sun in the sky. They move [on the clock face] mirroring the movement of the sun across the sky [so that they eventually] they descend and disappear with the setting of the sun. When night comes then there are planets that gradually emerge [to the observer] because of a light glowing from behind them. The [strength of the] light emitting from the discs of the planets [grows gradually and] reaches its fullest intensity on the completion of a full hour. Then this process begins in the next planet-disc and so on until the night ends and the sun begins to rise. In this way, you can know the times of the prayers.”
The phenomenon of the public display of beautiful and technologically sophisticated clocks was not confined to the Muslim East. Water clocks were also a common feature of urban life in the Maghrib, the Muslim West, which consists of Al-Andalus and the modern-day states of Morocco, Algeria, Tunisia, Libya and Mauritania. Like their counterparts in Syria and Iraq, the clocks of the Maghrib were almost always found in and around mosques and madrasas in the great cities of learning and culture, such as Fez, Marrakesh, Al-Qairawan and Tlemcen.
The Cordovan inventor Abbas Ibn Firnas (d.888), most famous for his experiments with gliders, built a water clock for the Umayyad Emir of Cordoba Muhammad I (d.886). It is mentioned in Al-Muqtabis min anba’ ahl al-Andalus by Abū Marwān Hayyān ibn Khalaf Ibn Ḥayyān al-Qurtubi (987–1075). The book was lost for a long time and was found only a few decades ago. The clock was called al-miqata (from the Arabic word al-miqat, which means the calculating of time); also called al-minqana. Ibn Firnas mentions it in the following three lines of poetry:
ألا إننـي للديـن خيــــــرُ أداةِ إذا غاب عنكم وقت كل صلاةِ
Verily I have rendered for the religion a valuable service [by inventing a device] for occasions when you cannot discern the prayer times [with the naked eye].
ولم تُرَ شمسٌ بالنهار ولم تُنِرْ كواكـب ليلٍ حالكِ الظلمــــات
When the sun is not visible during the day and in the darkness of the murkiest nights, when the stars do not even shine
بيُمن إمــــام المسـلمين محمد تجلت عن الأوقات كل صـلاة
By the good fortune of the Leader of the Muslims, Muhammad, [my invention] has made the times of all the prayers clear to see.
It can be inferred from this poem that the clock was constructed for the purpose of determining the times of the five daily prayers and that it was a water clock (clepsydra). This conclusion was arrived at due to the fact that this clepsydra was built to be used on cloudy days and during the night. This would imply that it was a water clock. Most significantly, for the history of clock-technology, this is the earliest reference to a water clock in Al-Andalus. We have no knowledge of any connections between Abbas ibn Firnas with neither Baghdad nor the clock technology that produced the Harun al-Rashid clock a few decades before.
Al-Zarqali (d.1011) constructs the clocks of Toledo, which were, to some extent, the predecessors of the clocks or planetary calendar devices that became fashionable six centuries later in Europe. He fled Toledo to Cordoba as the result conquest of Toledo by Alfonso VI of Castile in 1085.
In his Kitab al-Jughrafiya (Book of Geography), Al-Zuhri (d.mid 6th century Hijra) describes a water clock with two basins that marked the date of the lunar month that was built in Toledo by a certain Abul-Qasim b. A’bd al-Rahman, known as Al-Zarqal. Julio Samso doubts whether he was referring to the same Abu Ishaq Ibrahim b. Yahya Al-Zarqali. In view of the absence of any information on Al-Zarqal apart from Al-Zuhri’s mention, it might be that Al-Zuhri had confused the names. This is a subject requiring further research.
Al-Zuhri’s description of the famous clocks of Toledo was translated into Castilian by J.M. Millas-Vallicrosa. The clocks were in use until 1135 when King Alphonso VII tried to discover how they worked and asked Hamis Ibn Zabara to dismantle them. Once they were taken apart, nobody could reassemble them. They constituted a very precise lunar calendar and were, to some extent, the predecessors of the clocks or planetary calendar devices that became fashionable six centuries later in Europe.
In his “Nafh al Tib min Ghusn al-Andalus Al-Ratib wa Tarikh Lisanu din al-Khatib”, Aḥmad ibn Muḥammad al-Maqqarī gives a vivid account of the intricate working of the clocks as follows:
“The clocks consisted of two basins, which filled with water or emptied according to the increasing or waning of the moon. At the moment when the new moon appeared on the horizon, water would begin to flow into the basins by means of subterranean pipes, so that there would be at day-break the fourth of a seventh part, and at the end of the day half a seventh part, of the water required to fill the basins. In this proportion, the water would continue to flow until seven days and as many nights of the month had elapsed, by which time both basins would be half-filled. The same process during the following seven days and nights would make the two basins quite full, at the same time that the moon was at its full. However, on the fifteenth night of the month, when the moon would begin to wane, the basins would also begin to lose every day and night half a seventh part of their water, until by the twenty-first of the month they would be half empty, and when the moon reached her twenty-ninth night not a drop of water would remain in them. It is worthy of remark that, should anyone go to any of the basins when they were not filled, and poured water into them with a view to quicken its filling, the basins would immediately absorb the additional water and retain no more than the just quantity. On the contrary, were anyone to try, when they were nearly filled, to extract any or the whole of their water, the moment he raised his hands from the work the basins would pour out sufficient water to fill the vacuum in an instant”.
In his kitab al-asrar fi nataij al-afkar (‘The Book of Secrets about the Results of Ideas’), he gives instructions on the construction of 15 large water clocks, amongst other machines. It is the earliest extant Arabic language work on the construction of water clocks. According to Donald Hill, Al-Muradi invented the first geared clock, which was a water clock that utilised a complex gear train mechanism that included both segmental and epicyclic gearing, capable of transmitting high torque. Al-Muradi’s clocks were also the first to also employ mercury in their hydraulic linkages, which solved the problem of water behaving differently according to room temperature. Unfortunately, we know very little about his life, not even his date of birth or death.
His kitab al-asrar is a treatise on how to construct a wide variety of ingenious mechanical devices including 15 clocks. According to Donald Hill this book was written in mid.11th century. Its manuscript is preserved in the Biblioteca Medicea Laurenziana in Florence. This is the only known extant copy of the text, although it is unlikely that it is the original manuscript authored by Al-Muradi himself as the date of completion that is indicated on the manuscript as 21st Sha’ban 664 H (1266 CE).
Most of the 15 water clocks described by Al-Muradi are similar to those described by Ridwan al-Sa’ati and Al-Jazari in that they function through a floating orbit that descends slowly inside a water tank and operates, through its movement, all the gears. The hours are signalled by small metal balls, by the movement of automatons, or by the illumination of lanterns. Similar water clocks can be found in Al-Jazari’s treatise, which antedates Al-Muradi’s manuscript by nearly 60 years. Al-Jazari not only describes similar machines but mechanisms very similar to those in Al-Muradi’s treatise. These include the expulsion of balls and their transfer via tubes, as well as statues, snakes and the way in which they are loaded and expelled, which is the same as those found in Al-Jazari’s work, but of much larger sizes.
There is an original description of a clock in the palace of Abu Hammu II (1359-1389), Tlemcen, Algeria. This description is made by Abu Zakariyya Yahya b. Abi Bakr b. Khaldun, the less famous brother of the author of the Muqaddimma, in his work bughyat al-ruwwad fi dhikr al-muluk min Bani Abd al-Wad, which is a panegyric history of the Abd al-Wadid Sultans of Tlemcen. We do not know how it might have looked beyond what the imagination can glean from Abu Zakariyya b. Khaldun’s description. It is a rather vivid description nonetheless, from which we can surmise that the clock was in the style of the classic water clocks of Syria and Iraq. It carried all of the typical features; twelve doors to indicate the passing of each temporal hour, bird figures that deposited balls into metal bowls that chimed, holes in the metal bowls that allowed the balls to run back into the body of the clock, and a device that mirrored the movement of the moon across the sky. This Tlemcen water clock seems more sophisticated and opulent though, with its slowly climbing mechanical snake, the squawking silver eagle that reacts to the snake’s attack on its chicks, and the finely crafted figurine that appears on the hour to display the time in writing. These extra features are similar to those found in Al-Muradi’s clocks.
A spectacular water clock (Mangana) covering the wall of a building opposite to the Bou-‘Inania school, Fez, was commissioned by Sultan Al-Mutawakkil Abu ‘Inan. Its construction was completed on 3rd June 1357 approx. It was designed and constructed by its supervisor (muwaqqit) Ali b. Ahmad al-Tlemceni. Remnants of the exterior walls can be still be seen at Souq al-qasr in the old city of Fez.
The main feature of this clock is its large size, the number of windows, the loud chime of each hour, and that its daily hours change according to the seasonal length of each day. Full description and detailed drawings with 3D animation have been made by the Foundation for Science, Technology and Civilisation UK, and is the subject of a pending book by the present author.
Another but smaller indoor water clock was commissioned in the Qarawiyyin Mosque, Fez by Marinid Sultan Abu Salim in 1361. It was built by Abu Zayd Abd al-Rahman b. Sulayman al-Lajjai. The clock is extant and can be seen inside the Mosque at the Muwaqqit room. The clock is referred to as the Magana. a distinctive feature of the clock is that it has an in-built Astrolabe, it divides the day into 24 equal hours and that the metal balls are carried by a tray that moves along a track and progressively conveying them to 12 metallic cups through channels. The following is from a note found in the 1980s in the muwaqqit chamber:
“In the name of God, this Magana was built, along with the astrolabe that goes with it, at the orders of our master the Sultan Abu Salim, son of our master Abu al-Hasan, son of our master Abu Sa’eed, son of our master Abu Yusuf, son of Abd al-Haqq the Marinid. Its construction and installation was completed on the 21st of Muharram in the year 763 of the Hijri calendar (20 November 1361).”
A recent photograph of the exteriors of the clock inside the Muwaqqit room is shown on the top right Figure 10. The Astrolabe is visible next to the twelve metal cups on the top right. An old pendulum wall clock is seen mounted on the right. The mattress and cushion are where the Muwwaqit rests.
Recent attempts to restore the clock, based on extant remnants of the original clock, used a moving trolly to carry the metal balls and release them onto the 24 brass cups. The main reason is to allow easy access for loading the balls as the trolly gets to the end of the track.
For more information on Automatic Machines and clocks in Muslim Civilisation, see the paper by Salim Al-Hassani, The Journey of Automatic Machines in Muslim Civilisation, Muslim Heritage portal, Published on 24th October 2016.
Although we do not have a description of the clock’s inner workings that Harūn al-Rashīd gifted to Charlemagne, we could guess how it might have worked, thanks to a number of descriptions of other water clocks that were spread around the Muslim world prior to and after the 11th-12th century.
One of the detailed descriptions is by the famous theologian scholar Abū Ḥāmid al-Ghazālī (1058-1111) who was familiar with early water clocks. More famous for his magnum opus on Muslim spirituality, the Iḥyā ‘Ulūm al-Dīn (‘The Revival of the Religious Sciences), than for contributions in the field of physical sciences, Al-Ghazālī gave us, in his Arba’īn fī uṣūl al-dīn (Forty in the Tenets of the Religion), a detailed description of the inner workings of what could have been a typical water clock of his time. This could have been the basic mechanism that Harūn al-Rashīd’s clock had been based on, albeit some 200 years earlier. He says:
“Integral to the water clock is a large cylindrical tank containing a known measure of water. A hollow cylindrical vessel (i.e. a float) is placed into this cylindrical tank so that it floats on the surface of the water. A taut piece of string attaches this hollow cylindrical vessel to the underside of a trough that stands above the hollow vessel. Within the trough is a marble. Underneath this whole contraption is a round, shallow metal bowl so that when the ball falls it drops into the metal bowl, the impact creating a clanging sound. A hole of a known specific size is bored in the bottom of the large cylindrical tank so that the water inside it drips out bit by bit. Thus, as the level of the water inside the tank drops as the water exits through the hole, the bowl floating on the surface of the water inside the tank will drop accordingly. This causes the taught string to pull down on the trough containing the ball, causing it to tilt to one side until it tips over completely, and the ball rolls out, dropping into the metal vase below and causing a clanging sound as it strikes the vase. This happens once every hour. The length of time between one drop of the ball and another is determined by the rate at which the water drips out of the tank and the subsequent reduction of the water level within the tank. The rate at which the water drips from the cylinder depends on the size of the hole drilled in the bottom of the tank, out of which the water exits. The appropriate size of hole to be drilled is worked out by using calculation. Thus, the rate of exit of water from the tank is known precisely and is determined by appropriately calibrating the size of the hole. In this way, the descent of the hollow bowl floating on the water, its pulling on the string attached to the trough containing the ball, the tipping of the trough and its spilling the ball onto the bowl, is all determined by one ultimate causal factor that is totally regular, neither increasing or decreasing in any way.
The dropping of the ball into the bowl can even be used to cause another movement. This additional movement can then cause a third additional movement, which, in turn, can set off a whole chain of subsequent movements, of increasing complexity, until other most fascinating and wondrous movements are created. It is all, nevertheless, specifically calibrated and pre-determined. Its original cause is, quite simply, the exit of water from a vessel at a determined rate.” 
The modern scholar, M.A. Dahman, reproduces this passage. Interestingly, Al-Ghazali’s description of the functioning of a water clock did not come from a book on physics, mechanics, or clock making, but from his Arba’īn fī uṣūl al-dīn, a religious work dealing with Islamic belief. He used the water clock as a tangible example in order to explain the Islamic concept of divine decree and destiny (al-qaḍa wa’l-qadar), which he saw mirrored in the mechanical workings of water clocks. Although Al-Ghazali lived three centuries after Harun al-Rashid and one century before Al-Jazari, his use of this example indicates that such water clocks must have been widely used.
Another worthwhile description is that of the clock of Muhammad al-Sa’ati who built a monumental clock at the Jayrun Gate in Damascus, in the reign of Nur al-Din Mahmud b. Zanki in Damascus (reigned 1154–74). This makes it decades after Al-Ghazali’s departure from Damascus and eventual death. The clock was described in detail by his son Ridwan in a treatise Kitab ‘Amal al-sa’at wa-l-amal biha (On the Construction of Clocks and their Use) completed in 1203 CE.
There were a number of paintings showing a delegation of Harun al-Rashid holding what was envisaged as a clock, but unfortunately none of these tallies with the descriptions in historical documents. The nearest to it is a drawing given by Claudius Saunier depicts it in a drawing. However, this cannot be realistic either, as the picture does not show a space to accommodate a water tank, neither does it show a spout for the balls nor a bowl to receive them. Furthermore, the horses are shown to travel around a square path having to turn a right angle. In our opinion, the windows would have been in a raw and the clock would have a front face revealing the progressive emergence of the horses and the falling of the balls onto the cymbal.
There is an issue with this depiction. If we accept that the water tank was an integral part of the clock, then it would have to be small (comparable to the size of the clock body seen in the picture). In which case, for the water to empty at a realistic rate, the orifice at the base of the water tank would have had to be a small fraction of a millimetre in diameter; a challenging manufacturing problem for that time
A modern historian, Richard Hodges, refers to it as a brass clock and reports that in 807, the Emperor’s biographer, describes the clock as a
“marvelous mechanical contraption, in which the course of the twelve hours moved according to a water clock, with as many brazen little balls, which fell down on the hour and through their fall made a cymbal ring underneath. On this clock there were also twelve horsemen who at the end of each hour stepped out of twelve windows, closing the previously open windows by their movements.”
Ulrich Alertz, recently (2010) wrote a chapter on “The Horologium of Harun al-Rashid, Presented to Charlemagne: An Attempt to Identify and Reconstruct the Clock Using the Instructions provided by Al-Jazarī ”. Despite the fact that there were 400 years between Harun al-Rashid and Al-Jazari, the author assumes that Al-Jazari’s castle clock would have been similar to Harun al-Rashid’s clock and uses Al-Jazari’s description of his castle clock to explain the mechanism and working principle of Harun al-Rashid’s clock. Although this is an excellent attempt, we believe this is a challenging assumption as there must have been numerous developments during that period. A full description with 3D modelling of Al-Jazari’s castle clock is given by the present author. Besides, some of the features such as horsemen, single spout for the falling balls, the absence of musicians’ automatons and falcons and the challenge of size and the need for transportation make them different.
Much data on various water clocks were collated in order to make engineering sense from these various descriptions to assist in predicting the mechanism of Harun Al-Rashid’s clock. The envisioned appearance and construction of the Harun clock are drawn using engineering graphics software. We guess that afloat, semi-submersed in large water outflow clepsydra would have controlled the clock. As the water escapes out of the lower base of the tank, the float moves down pulling with it a rope that moves a small cart via a pulley. As time passes, the cart moves along a rail it trips a series of already primed 12 windows and releases small metal balls. At the same time, a toy Arabian Knight on a horse emerges from each window. The train of events continues for 12 hours when the tank empties of water. On the hour a metal ball falls onto a brass vase generating sound. Simultaneously, the window doors open, and a horseman emerge. After 12 hours have passed, there will be 12 horsemen outside the 12 windows and 12 balls will have been collected in a receiving box next to the ringing bowl. At the end of the day, the clock is reset by sliding the cart back, pulling back the horses, the dead weights for the doors are reset, doors are shut, balls are placed in the tray, and the main float is lifted to allow refill of the water tank.
One would expect the rear of the clock would have been covered by a light removable box to avoid dust and for cosmetic reasons.
An attempt is made to construct a virtual model of this clock based on historical evidence combined with what is thought to be mechanically feasible by the technology in Baghdad at the time and the constraints of transportation as well as the need for assembling and maintenance. The figures show the front view and working mechanism of the proposed model. The size could be made large but there is a limit to how small it can be. This is governed by the need for a minimum size of the float to drive the trolley along the rail, which would decide the diameter of the water tank and a minimum height for the float to travel and pull through the trolley across the width of the clock over twelve hours duration. Although the reports refer to it as a brass clock, we believe it could not have been entirely brass as it would have been too heavy to transport. Furthermore, we introduced a tray mounted on a sliding saddle. This would have been probably used to provide ease of loading of the brazen balls. However, as it will be seen later, neither Ridhwan nor Al-Jazari used this feature, but we see it in the clock of the Qarawiyyin Mosque in Fez.
An important feature of the clock is not mentioned in the descriptions of the clock. A water clock usually requires a steady linear steady flow of the water so that time can be measured at equal intervals. This is achieved by either tapering the side of the tank into a parabolic shape or by introducing a flow regulator valve at the orifice. We notice Al-Muradi used a tapering tank. Ridwan and Al-Jazari, however, used a floating valve system. The system was frequently used by Banu Musa in their trick devices. It is similar to the carburettor system of the modern car that regulates the flow of the gasoline. The purpose of this floating valve system was to keep water flowing out of the main tank at a constant rate and independent of level and pressure deviations.
The diagrams shown depict pictures from the 3D model. The clock would have been boxed-in with the front face showing the doors, the toy horsemen and the bowl. The setting up and the operation as well as resetting the clock can be easily worked out from the diagrams.
No dimensions are indicated as these will depend on the overall size and weight of the clock to be manufactured. The Foundation team already has manufacturing drawings for future use whether to construct a portable model or a large size monument such as the Al-Jazari’s castle clock built at Ibn Battuta Mall, see figure below:
This work is the result of a dedicated effort of the team of the Foundation for Science, Technology and Civilisation, and friends, in particular Abdel Kader Jahjah, Wai Yin Chang and Jonathan W. B. Chang and Bilal Sabbagh.
There are numerous friends and supporters who assisted in various ways during the author’s field visits to Baghdad Dar Al-Hikmah, Damascus Umayyad mosque, Jizra and Diyar Bekir, Fez Al-Qarawiyyin mosque and the Madrassah Bou-Inania. Last but not least thanks and appreciation go to late Dr Abdel Hadi Al-Tazi of Fez who provided guidance and original documents on the Fez clocks.
 Hodges, R. (1983). Mohammed, Charlemagne, and the Origins of Europe. N.Y: Ithaca, pp. 121.
 Heck, G.W. (2007). When Worlds Collide: Exploring the Ideological and Political Foundations of the Clash of Civilisations. Lanham, M.D.: Rowman and Littlefield, pp. 172-173.
 Hodges, R. Mohammed, Charlemagne, and the Origins of Europe, Opcit. p. 121.
 McKitterick, R. (2008). Charlemagne: The Formation of European Identity. Cambridge, p. 287.
 Mandaville, J. (1977). An Elephant for Charlemagne. Saudi Aramco World, vol. 28, No. 2, pp. 24-27; p. 27.
 “Suite Des Usages Du Temps De Charlemagne. Commerce, Finances, Sciences.” In Voltaire: Oeuvres Complètes — 109 Titres Et Annexes (Annotées), 7885.
 Sholz, B.W. & Rogers, B. tr. (1972). Carolingian Chronicles: Royal Frankish Annals and Nithard’s Histories. M.I: Ann Arbor, p. 87.
Also see: http://babel.hathitrust.org/cgi/pt?id=mdp.39015015186805;view=1up;seq=97
If you go to page 81 it will take you to the entry for the year 801 AD, which is when the first mention of envoys from Harun al-Rashid occurs.
 Wood, E.J. (1866). Curiosities of Clocks and Watches from the Earliest Times. Hutchinson, pp.11-13 (from a digital version of the original kept in the University of Wisconsin Library)
 World Heritage Encyclopaedia, History of Time Keeping Devices,
 D. R. Hil, A History of Engineering in Classical and Medieval Times (London, 1984), p. 213.
 A qanat is one of a series of well-like vertical shafts, connected by gently sloping tunnels. They create a reliable supply of water for human settlements and irrigation in hot, arid and semi-arid climates. See Andrew Wilson: “Hydraulic Engineering and Water Supply”, in: Handbook of Engineering and Technology in the Classical World, edited by John Peter Oleson (New York: Oxford University Press, 2008), p. 291 ff; and Paul Ward English, “The Origin and Spread of Qanats in the Old World,” Proceedings of the American Philosophical Society, vol. 112 (1968), pp. 170-181.
 D.R. Hill, Arabic Water Clocks, pp.7-8
 Evliya Çelebi, Günümüz Türkçesiyle Evliya Çelebi Seyahatnamesi: İstanbul, Hazırlayanlar: Seyit Ali Kahraman-Yücel Dağlı, Yapı Kredi Yayınları, 1st ed. 2003, 5th ed. 2008 ISBN 978-975-08-0564-X
 Ibid, pp.8
 H. Fragaki, “Clocks and Dials with Automata: The Mosaic of Qasr al-Lebya,” in T. Koetsier and M. Ceccarelli (eds.), Explorations in the History of Machines and Mechanisms, (Berlin: Springer, 2012), p. 232.
 Vitruvius: ten books on architecture, Translation [from Latin] by Ingrid D Rowland; commentary and illustrations by Thomas Noble Howe; with additional commentary by Ingrid D Rowland and Michael J Dewar, ed. I D Rowland, N Howe, and M J Dewar.1999, Cambridge, New York Cambridge University Press.
 W S Eichelberger, Clocks – Ancient and Modern. Science, 1907. 25(638), pp. 441-452.
 See D.R. Hill, Arabic Water Clocks, pp. 15-34.
 H. Fragaki: ‘Clocks and Dials with Automata: The Mosaic of Qasr El-Lebya’, Opcit p. 232.
 Ibid, p. 233.
 Joseph Needham, Wang Ling and Derek j. de Solla Price, Heavenly Clockwork.
The Great Astronomical Clocks Of Medieval China, published in association with the antiquarian horological society, University Press, 1960
 Joseph Needham, Science and Civilization in China:, Volume 4, Part 2, Mechanical Engineering,.
 D.D. Leslie: Islam in Traditional China: A Short History to 1800. Belconnen, A.C.T. Canberra College of Advanced Education, 1986, p. 32.
 D.D. Leslie: The Integration of Religious Minorities in China: The Case of Chinese Muslims; The Fifty-ninth George Ernest Morrison Lecture in Ethnology 1998. At http://chinainstitute.anu.edu.au/sites/default/files/morrison59.pdf
 See, e.g., the Buddhist traveller Hui-chao (ca 727), who wrote that the Arabs worshipped Tian (Heaven), and did not know the Buddha; and Du Huan (captured at the Battle of Talas in 751 and taken to Baghdad), who gave a short account of Islam, ‘the Arab doctrine’. See Leslie, Islam, pp. 20-22.
 Jun-yan, Zhang. (1980) “Relations Between China and the Arabs in Early Times,” Journal of Oman Studies 6: 91-109.
 H.A.R. Gibb: The Arab Conquests in Central Asia, London, 1923, esp., pp. 11-13.
 S E Al-Djazairi. (2019) ”Islam in China”, MSBN Books.
 Al-Qazwini cited in Al-Hassan and Hill, Islamic Technology, p. 191.
 M. Lombard: The Golden Age of Islam; tr., J. Spencer (North-Holland Publishers; 1975), p. 192.
 In D. Hunter: Papermaking: The History and Technique of an Ancient Craft (Pleiades Books; London; 1943; 1947), p. 139; p. 471.
 Joseph Needham, Science and Civilisation in China, 6(3), Cambridge University Press, 1996, pp. 9, 11, 13, 32, 33, 36.
 1001 Inventions: The Enduring Legacy of Muslim Civilization: Reference (4th) Edition Annotated, Text only. FSTC Ltd, Kindle Edition, https://www.amazon.co.uk/1001-Inventions-Civilization-Reference-Annotated-ebook/dp/B0775TFKVY
 Al-Jahiz, Amru ibn Bahr: Kitab al-Haywan, edited by Abdul Salam Harun, Vol. 2, Published by Dar Al-Jeel, (1996). Also page 74, Vol II of the Beirut Edition, 1992.
 Salim Al-Hassani, “The Mechanical Water Clock of Ibn Al-Haytham,” permanent URL: https://muslimheritage.com/the-mechanical-water-clock-of-ibn-al-haytham/
 Nabila A. Dawood, Scholarly Traditions of the Schools in Baghdad: The Mustansiria as a Model,http://www.muslimheritage.com/article/scholarly-traditions-schools-baghdad-mustan%E1%B9%A3iria-model. Prof. N A Dawood refers to the following primary sources confirming the diversity of the curriculum including natural science topics:
– Al-Futi, Abdul Razzaq bin Mhd bin Ahmad, Al-Hawadith al-Jamia’a wal Tajarub Al-Nafia’ah fil Miatul Al-Sabia’ah, Edited by Mustafa Jawad, Baghdad, (1351 AH) p 58
– Al-Irbilli, Sinbut Qanito: Khulasatul Dahab al-Masbook, Publ. Muthannah Library, Baghdad, (1964), pp 286-287.
– Al-Dhahabi, Mhd ibn Ahmed ibn Othman: Ibn Al-Jazari, Al-Mukhtar min Tarikh Ibn Al-Jazri, Edited by K.A Al-Minshawi, Dar Al-Kitab Al-Arabi, Beirut, (1988), p 150.
 Ibn Battuta: Tuhfat al-andhar fi gharaaib al-amsar wa ajaaib al-asfar (Cairo, 1904) pp.167-168
 Source: https://muslimheritage.com/mustansiria-model/. Also http://www.davidmus.dk/en/collections/islamic/dynasties/late-abbasids/architecture/mustansiriya-madrasa. Photo Hans Munk Hansen
 Lucknawī, Muḥammad ‘Abd al-Ḥayyī. Al-Fawā’id al-bahiyya fi tarājim al-Ḥanafiyya. Publ. Al-Saa’dah, Egypt, (1967). P.26
 M.A.Dahman, ‘ilm al-Sa’at, pp.38 – from Abd al-Razzaq ibn Taj al-Din Ibn al-Futi: al-Hawadith al-jami’a wal-tajarub al-nafi’a fi al-mi’a al-sabi’a, edited by Mustafa Jawad, (Baghdad, 1932), pp.82
 Abū Marwān Hayyān ibn Khalaf Ibn Ḥayyān al-Qurtubi. (1937). Al-Muqtabis min anba’ ahl al-Andalus, edition by Būlus Kitnar, Paris: Series “Textes arabes relatifs a l’histoire de l’Occident musulman”, N° 3.. See also the edition of the other volume by Abd al-Rahman al-Hajji. (1965). Beirut. See also the edition by Makkî, M.A. (1973). Beirut, pp. 282-284.
 Vernet, J. (1970-1980). ‘Abbas ibn Firnas’, Dictionary of Scientific Biography. vol. 1. New York, p. 5;
Hill, D.R. (1992). ‘Technologià Andalusi’ Legado Andalusi. Madrid. pp.157-172, pp. 163; Samsó, J. (1998). Las ciencias de los antiguos en al-Andalus, (Madrid, 1992); J.Casulleras, ‘The contents of Qasim ibn Mutarrif al-Qattan’s Kitab al-hay’a’, in M. Fierro and J. Samso (eds.). The Formation of al-Andalus, Part II: Language, Religion, Culture and the Sciences. London, pp. 55-56.
 Dawson, C. (1953). Medieval Essays. London: Sheed and Ward, pp. 129
 Al-Zuhri, Mohammed bin Abi Bakr. Kitab al-Jughrafiyya (Book of Geography), ed. Mohammed Hajj-Sadiq, sections 217-218 on Toledo. Port Said: Maktabat al-Thaqafah al-Diniyyah.
 Samso, J. al-Zarqali, Encyclopedia of Islam (2nd edition). Brill.
 Millas-Valiscrosa, J.M. (1943-1950). Estudios Sobre Azarquiel. Madrid/Granada, pp. 6-9.
 Vernet, J. (1970-1980). ‘al-Zarqali’, Dictionary of Scientific Biography, Vol. 14. New York, pp. 592.
 Ibid, pp. 592-593.
 Al-Maqqari, tr. by Gayangos, P. (1840-3). Nafh Al-Tib: The History of the Mohammedan Dynasies in Spain. London: The Oriental Translation Fund, Vol I, pp. 81-83.
 Hill, D.R. (1996). A History of Engineering in Classical and Medieval Times. Abingdon (UK), p. 203.
Hill, D.R. Arabic Water Clocks, p. 37. The portable universal sundial may have been an addition to the original source. See Julio Samsó’s review of the Italian edition and translation (into English) in Suhayl 9 (2009-10), pp 234-238.
 Introduction to the English version of ‘The Book of Secrets in the Results of Ideas’, edited by Leonardo Research Centre for the Qatar Museums Authority, p.11
 Hill, D.R. Arabic Water Clocks, p.39
 ‘The Book of Secrets’, p.23
 Salim Al-Hassani, Al-Jazari’s Castle Water Clock: Analysis of its Components and Functioning, https://muslimheritage.com/al-jazaris-castle-water-clock/ Published on: 13th March 2008.
 Abu Zakariyya Yahya b. Abi Bakr Muhammad b. Muhammad b. Hasan b. Khaldun. (1980). Bughyat al-ruwwad fi dhikr al-muluk min Bani Abd al-Wad. 2 vols. Algeria.
 A.M.Dahman: ilm al-Sa’at, pp.44
 Salim T S Al-Hassani, “1001i Machines and Devices from Muslim Civilisation”, Foundation for Science and Civilisation UK, to be published.
 Source: Ahmed Salim, 1001inventions.com. Also see Salim Al-Hassani, The Journey of Automatic Machines in Muslim Civilisation, https://muslimheritage.com/journey-of-automatic-machines/. Published on 24th October 2016.
 L. Kotthoff, “Wasseruhr mit 24-Studen-Einteilung”, Nachbau des Originals aus dem 12 Jahrhubdert (Fes/Marokko). Also see Derek de Solla Price “Mechanical Water clock in the 14th century in Fez Morocco” Ithaca, 26, VIII-2 IX (1962) Hermann Paris pp599-602.
 Al-Ghazali, A.H. (1910). Arba’in fi usul al-din. Cairo: al-Matba’a al-Tijariyya, p. 13 .
 Dahman, M.A. (1981). Muqaddimat ‘ilm as-sā’āt wa’l-‘amal biha. Damascus, pp. 20-21.
Saunier, C. (1903). Die Geschichte der Zeitmesskunst. Bautzen: Emil Hübners Verlag, p.165.
 Hodges, R. (2000). “Charlemagne’s Elephant”. History Today.
 Alertz U., ed. Zielensnki S. et.al (2010). The Horologium of Harun al-Rashid, presented to Charlemagne: An Attempt to Identify and Reconstruct the Clock Using the Instructions Provided by Al-Jazarī, in Variantology 4, “On Deep Time Relations of the Arts, Sciences and Technologies in the Arabic-Islamic World and Beyond”. Konig: Buchhandlung Walther Konig GmbH & Co. KG. Abt. Verlag. pp. 19-42.
 Salim Al-Hassani, (2008). ‘Al-Jazari’s Castle Water Clock: Analysis of its Components and Functioning’. [Online] Available at: http://www.muslimheritage.com/article/al-jazari%E2%80%99s-castle-water-clock-analysis-its-components-and-functioning, published 13 March 2008.