Khorasan (khôrˌəsänˈ) [key] or Khurasan kŏrˌəsänˈ, region and former province (1991 pop. 6,013,200), c.125,000 sq mi (323,750 sq km), NE Iran. Mashhad is the chief city; other cities include Sabzevar, Bojnurd, and Neyshabur. It is mainly mountainous and arid. Khorasan was occupied by the Arabs in the mid-7th cent., and Abu Muslim began (8th cent.) his campaign against the Umayyads there. The province contributed to the power of the early Abbasid caliphs. Khorasan was devastated by the Oghuz Turks in 1153 and 1157 and by the Mongols from 1220 to 1222. Timur invaded in 1383. An earthquake devastated Khorasan in 1997. In 2004 Khorasan was divided into three provinces: Northern, Southern, and Razavi Khorasan.