According to Toxel.com:
Shibam, a town in Hadramawt, Yemen, is considered to have the world’s oldest skyscrapers. It has about 7,000 inhabitants and all of the town’s house are made out of mud bricks. Some of these structures rise 5 to 9 stories high.
This technique of building was implemented in order to protect residents from Bedouin attacks. While Shibam has existed for around 2,000 years, most of the city’s houses come mainly from the 16th century.