Bosra Citadel lies in the city of Bosra in Syria.
Bosra Citadel is a peculiar building. It started out as a Roman amphitheatre which was built in the late 2nd century. It can accommodate something between 9000 and 15.000 spectators. Probably during the reign of the Umayyads (7th and 8th century) all the portals of the amfitheatre were walled up.
During the time of the Abbasids the building was used as a refuge. After the Seljuk Turks had conquered Damascus and the surrounding area in 1076, they were the first to transform the building into a real citadel. Two staircases were built into towers and all openings were walled up.
Around 1202/03 Bosra Citadel was strenghtened once more by the Ayyubids under Saladin's brother; Al-Adil. Up to 9 massive square towers were built around the inner core of the citadel projecting from blind ramparts. The entire complex was circled by a deep ditch. Inside an iron-bound gate, series of vaulted rooms, twisting passages, rampart walks and all kinds of defensive works were built. Building material was taken from the remains of the antique Roman city behind it as you can see from the sections of pillars used to strengthen the walls of the towers.
After the death of Al-Adil in 1218, his son as-Salih Ismail used Bosra Citadel as his residence until 1246. In 1260 the citadel was given over to the Mongols without a fight. Not much later the Mongols were driven out by the Mamluk Sultan Baibars. He restored the citadel and stationed a garrison there. This garrison continued its existance well into the Ottoman empire and even in 1897 consisted of several hundred men.
During the 20th century the Syrian Department of Antiquities restored the Bosra Citadel and uncovered the Roman theater by removing all the medieval additions inside it.
At present Bosra Citadel can be visited for a small fee. It's a great and unique mix of a military citadel and a Roman amphitheatre. You can freely explore all the hallways and rooms, recommendable.