Lying in the desert east of Amman are a number of desert castles built or restored in the seventh and eighth centuries by the Umayyad caliphs. Constructed as both retreats of pleasure and bastions of protection they stand as a memorial to the early days of the Arab Empire. Known collectively as the Desert Castles or Desert Palaces, the buildings demonstrate the best of early Islamic ingenuity. These are some of the most well known castles, Qasr Hallabat, Qasr Azraq, Qasr Amra, Qasr Mushatta, Qasr Muwaqqar, Qasr Kharana, Qasr Ain es Sil, Qasr Qastal. In addition there is several fumous castles in the mountains, such as Rabad and Karak.