NISIBIS (NUSAYBIN), a frontier fortress and trading town of Turkey on the Syrian border about 13o m. N.W. of Mosul, Iraq. It lies on the borderland between the mountains and the plain in 37° N. 41° E. at the point where the Yaghyagha (called in ancient times the Mygdonius) passes through a narrow canyon and enters the plain. In ancient times, and indeed until the iith century A.D., the plain regions below the town are said to have been wooded and the town was famous for its agricultural products. Strategically, like Edessa (q.v.) it commanded the entrance of the valley country from the mountains and has been the site of fighting since Assyrian times to even as late as the 19th century. It also lies on the upper trade route from Mosul to the west and in times of peace has been of importance on this line.
Nisibis has been directed east or west according to the dom inant empire of the time. During the Assyrian empire it formed a frontier fort against aggressions from the north, and occupied a similar position in Seleucid times. From the middle of the
second century B.C. until the early years of the Christian era it was the residence of the kings of Armenia. Owing to its strength the fortress was of considerable importance during the struggle between Rome and Parthia. It became in early Christian times a religious centre with a Nestorian and a Jacobite bishop. Under the Caliphs it was a frontier fortress and the scene of continuous fighting. Finally it lost most of its prosperity owing to internal troubles, and according to the Arab chroniclers, the compulsory substitution of wheat for fruit crops. It is probable that an in sufficient control of the Bedouins of the desert was responsible for much of Nisibis' lost prosperity. To-day it is still a large town of probably over 50,000 inhabitants and the railway to Konia has rendered the site of significance.