The Mongol period was as eclectic in religious matters as it was in cultural and artistic ones. While the Mongols believed in shamanism, they embraced other religions for several reasons, ranging from a personal desire for the spiritual to issues of control and political and social cohesion. The century of Ilkhanid domination in Greater Iran witnessed the practice of Buddhism, Manichaeism, Zoroastrianism, Judaism, Christianity, and Islam.
The Mongols of the steppes believed in shamans—spiritual guides who could intercede between humans and the powerful spirits of good and evil. Both Genghis Khan (d. 1227) and his son Ögödei (r. 1229–41) were shamanists. One of Genghis’s grandsons, Khubilai Khan (r. 1260–95), embraced Buddhism, which was also officially adopted in Iran and Iraq under his brother Hülegü (r. 1256–65), founder of the Ilkhanid dynasty. Buddhism grew strong in Iran under Arghun (r. 1284–91). Christianity was popular with Ilkhanid women: Hülegü’s wife was a Nestorian and Arghun’s son (later Il-Khan Uljaitu) was baptized Nicholas in honor of Pope Nicholas IV (papacy 1288–92), who had sent several envoys inviting Arghun to convert to Christianity. Jews were prominent and formed significant communities at Isfahan and Hamadan. The powerful vizier Rashid al-Din (d. 1318) was a Jewish convert and his interest in Judaism is reflected in his Jami’ al-tavarikh (Compendium of Chronicles). After the conversion of Arghun’s son Ghazan (r. 1295–1304) to Islam in 1295, Buddhism lost its hold in western Asia. Ghazan encouraged theological debates primarily between the Sunni and the Shi’i approaches to Islam. These debates grew more active under Ghazan’s successor Uljaitu (r. 1304–17), who officially converted to Shi’i Islam in 1310. Sunni authority was reinstated under the reign of his son Abu Sa’id (1317–35).
Virtually nothing is left of Ilkhanid religious art and architecture from the period before the conversion to Islam. After Ghazan’s conversion, an aggressive program of construction and decoration of mosques was undertaken, while tolerance toward Shi’i Islam and Sufism promoted the building of tombs and shrines devoted to Sufi saints. The best Iranian craftsmen produced mosque furniture and furnishings ; ; . Large-scale luxurious Qur’an manuscripts were commissioned for religious institutions. Ilkhanid manuscript illustrations provide rare examples of representations of the prophet Muhammad and his companions, probably influenced by the circulation of Christian, especially Armenian, illustrated gospels and by the eclectic approach to religion in Iran at the time.