Shibam, the 16th-century city in Yemen, consisted entirely of over 500 high-rise tower houses. Why were the houses built that way? For defense! The houses of Shibam are all made out of mud brick and rise 5 to 11 stories high, with each floor having one or two rooms. This architectural style was used in order to protect residents from Bedouin attacks. Shibam is listed as UNSECO World Heritage Site.