Opposite the Roman theatre stood the citadel, or Jebel al-Qalaal, which throughout the first millennium AD kept watch from behind its ramparts over the population of Philadelphia (the city's name at that time). Of this fortified city, there remain vestiges of its outer walls, a temple of Hercules built in the 3C, a Byzantine church and an 8C Umayyad palace. Next to the temple, the Amman archaeological museum is invaluable in helping visitors develop a better understanding of the country.