TUSI, NASIR AL-DIN AL-

born Feb. 18, 1201, Tus, Khorasan [now Iran] died June 26, 1274, Baghdad, Iraq in full Muhammad ibn Muhammad ibn al-Hasan al-Tusi outstanding Persian philosopher, scientist, and mathematician. Educated first in Tus, where his father was a jurist in the Twelfth Imam school, the main sect of Shi'ite Muslims, al-Tusi finished his education in Neyshabur, about 75 kilometers (50 miles) to the west. This was no doubt a prudent move as Genghis Khan (d. 1227), having conquered Beijing in 1215, turned his attention to the Islamic world and reached the region around Tus by 1220. In about 1227 the Isma'ilite governor Nasir al-Din 'Abd al-Rahim offered al-Tusi sanctuary in his mountain fortresses in Khorasan. Al-Tusi in turn dedicated his most famous work, Akhlaq-i nasiri (1232; Nasirean Ethics), to the governor before being invited to stay in the capital at Alamut, where he espoused the Isma'ilite faith under the new imam, Alauddin Muhammad (reigned 12271255). (This Isma'ilite state began in 1090 with the conquest of Alamut by Hasan-e Sabbah and ended with the fall of the city to the Mongols in 1256.) During this period, al-Tusi wrote on Isma'ilite theology (Tasawwurat; Notions), logic (Asas al-iqtibas; Foundations of Inference), and mathematics (Tahrir al-Majisti; Commentary on the Almagest). With the fall in 1256 of Alamut to Hleg Khan (c. 12171265), grandson of Genghis Khan, al-Tusi immediately accepted a position with the Mongols as a scientific adviser. (The alacrity with which he went to work for them fueled accusations that his conversion to the Isma'ilite faith was feigned, as well as rumours that he betrayed the city's defenses.) Al-Tusi married a Mongol and was then put in charge of the ministry of religious bequests. The topic of whether al-Tusi accompanied the Mongol capture of Baghdad in 1258 remains controversial, although he certainly visited nearby Shi'ite centres soon afterward. Profiting from Hleg's belief in astrology, al-Tusi obtained support in 1259 to build a fine observatory (completed in 1262) adjacent to Hleg's capital in Maragheh (now in Azerbaijan). More than an observatory, Hleg obtained a first-rate library and staffed his institution with notable Islamic and Chinese scholars. Funded by an endowment, research continued at the institution for at least 25 years after al-Tusi's death, and some of its astronomical instruments inspired later designs in Samarkand (now in Uzbekistan). Al-Tusi was a man of exceptionally wide erudition. He wrote approximately 150 books in Arabic, Persian, and Turkish and edited the definitive Arabic versions of the works of Euclid, Archimedes, Ptolemy, Autolycus, and Theodosius. He also made original contributions to mathematics and astronomy. His Zij-i Ilkhani (1271; Ilkhan Tables), based on research at the Maragheh observatory, is a splendidly accurate table of planetary movements. Al-Tusi's most influential book in the West may have been Tadhkirah fi 'ilm al-hay'a (Treasury of astronomy), which describes a geometric construction, now known as the al-Tusi couple, for producing rectilinear motion from a point on one circle rolling inside another. By means of this construction, al-Tusi succeeded in reforming the Ptolemaic planetary models, producing a system in which all orbits are described by uniform circular motion. Most historians of Islamic astronomy believe that the planetary models developed at Maragheh found their way to Europe (perhaps via Byzantium) and provided Nicolaus Copernicus (14731543) with inspiration for his astronomical models. Today al-Tusi's Tajrid (Catharsis) is a highly esteemed treatise on Shi'ite theology. He made important contributions to many branches of Islamic learning, and under his direction Maragheh sparked a revival of Islamic mathematics, astronomy, philosophy, and theology. In the East, al-Tusi is an example par excellence of the hakim, or wise man.