The Muslim conquest of Khuzestan took place in 639 AD under the command of Abu Musa al-Ash'ari from Basra, who drove the Persian satrap Hormuzan out of Ahvaz. Susa later fell, so Hormuzan fled to Shushtar. There his forces were besieged by Abu Musa for 18 months. Shushtar finally fell in 642 AD; the Khuzistan Chronicle records that an unknown Arab, living in the city, befriended a man in the army, and dug tunnels through the wall in return for a third of the spoil. The Basrans purged the Nestorians—the Exegete of the city and the Bishop of Hormizd, and all their students—but kept Hormuzan alive.