Re-conquered by the Eastern Roman Empire in 533-534, it continued to serve as an Eastern Roman regional center, as the seat of the praetorian prefecture of Africa (after 590 the Exarchate of Africa). The city was sacked and destroyed by Umayyad Arab forces after the Battle of Carthage in 698 to prevent it from being reconquered by the Byzantine Empire. A fortress was built on the site and garrisoned by Muslim forces until the Hafsid period, when it was captured by Crusaders during the Eighth Crusade. After the withdrawal of the Crusaders, the Hafsids decided to destroy the fortress to prevent any future use by a hostile power. Roman Carthage was then used as a source of building materials for Kairouan and Tunis in the 8th century.