Striking for its barren desert location, its orange walls rising seemingly from nothing, this castle was built in around 700 A.D. by the Umayyads, Islam’s first dynasty. The fortress served both as a stop on caravan routes from Mesopotamia to Syria, and as an outpost to maintain control in a region once menaced by tribal wars. The site is fascinating for its bizarre amalgamation of Byzantine, Mesopotamian, Persian, and local architectural styles, and for its minaret, the third oldest in Islam, to which curiously no mosque has been attached. Well worth the short detour from Palmyra.