According to legend the city of Merv was founded by Alexander the Great in 330 BCE. Merv is by the Murgeb River, an oasis on a trade route in the Kara Kum desert – a route described as the Silk Road. A part of the Sassanid Empire for 400 years, it was home to Buddhists and Manichaeans, and in the 400s it was the seat of a Christian archbishopric of the Nestorian Church. Sassanid rule ended when King Yazdegerd III (633-651) was murdered near Merv and the Sassanian military governor surrendered to an Arab army. It was the seat of Arab rule in Khorasan and the center where the overthrow of the Umayyad caliph first gathered force – around the year 748.