(full name: Muʾayyad (al‐Milla wa‐) al‐Dīn (Muʾayyad ibn Barīk [Burayk]) al‐ʿUrḍī (al‐ʿĀmirī al‐Dimašqī) (مؤيد (الملة و) الدين (مؤيد ابن بريك) ألعرضي (العامري الدمشقي d. 1266) was a medieval Arab astronomer and geometer.
Born circa 1200, presumably (from the nisba al‐ʿUrḍī) in the village of ʿUrḍ in the Syrian desert between Palmyra and Resafa, he came to Damascus at some point before 1239, where he worked as an engineer and teacher of geometry, and built instruments for al-Malik al-Mansur of Hims. In 1259 he moved to Maragha in northeastern Iran, after being asked by Nasir al-Din al-Tusi to help establish the Maragha observatory under the patronage of Hulagu. Al-Urdi’s most notable works are Risālat al-Raṣd, a treatise on observational instruments, and Kitāb al-Hayʾa (كتاب الهيئة), a work on theoretical astronomy. His influence can be seen on Bar Hebraeus and Qutb al-Din al-Shirazi, in addition to being quoted by Ibn al-Shatir. Al-Urdi contributed to the construction of the observatory outside of the city, constructing special devices and water wheels in order to supply the observatory, which was built on a hill, with drinking water. He also constructed some of the instruments used in the observatory, in the year 1261/2. Al-Urdi’s son, who also worked in the observatory, made a copy of his father’s Kitāb al‐Hayʾa and also constructed a celestial globe in 1279.