composed his celebrated catalogue of ecclesiastical writers. The disorders and dissensions, which arose in the sixth century in the school of Nisibis, favoured the development of its rivals, especially that of Seleucia; however, it did not really begin to decline until after the foundation of the School of Baghdad (832). Notable people associated with the school include its founder Narses; Abraham, his nephew and successor; Abraham of Kashgar, the restorer of monastic life; and ArchbishopElijah of Nisibis. As a fortified frontier city, Nisibis played a major role in the Roman-Persian Wars. It became the capital of the newly created province of Mesopotamia after Diocletian's organization of the eastern Roman frontier. It became known as the "Shield of the Empire" after a successful resistance in 337–350. The city changed hands several times, and once in Sasanian hands, Nisibis was the base of operations against the Romans. The city was also one of the main crossing points for merchants, although elaborate counter-espionage safeguards were also in place. Islamic period The city was taken without resistance by the forces of the Rashidun Caliphate under Umar in 639 or 640. Under early Islamic rule, the city served as a local administrative centre. In 717, it was struck by an earthquake and in 927 it was raided by the Qarmatians. Nisibis was captured in 942 by the Byzantine Empire but was subsequently recaptured by the Hamdanid dynasty. It was attacked by the Byzantines once again in 972. Following the Hamdanids, the city was administered by the Marwanids and the Uqaylids. From the middle of the 11th century onwards, it was subjected to Turkish raids and being threatened by the County of Edessa, being attacked and damaged by Seljuq forces under Tughril in 1043. The city nevertheless remained an important centre of commerce and transport. In 1120, it was captured by the Artuqids under Necmeddin Ilgazi, followed by the Zengids and Ayyubids. The city is described as a very prosperous one by the period's Arab geographers and historians, with imposing baths, walls, lavish houses, a bridge and a hospital. In 1230, the city was invaded by the Mongol Empire. Mongol sovereignty was followed by that of the Ag Qoyunlu, Kara Koyunlu and Safavids. In 1515, it was taken by the Ottoman Empire under Selim I thanks to the efforts of Idris Bitlisi. Modern history On the eve of World War I, Nusaybin had a Christian community