en.wikipedia.org/wiki/Yemen

For centuries the need for security has driven the fiercely tribal inhabitants of Yemen to live together in towns that can be easily defended. Although there are distinct regional differences, the vernacular house is a tower, built to a height of up to 30 metres. Sana’a, the capital of the Yemen, has about 14000 of these tower houses. Typically they are six storeys high, made of mud bricks decorated with thick layers of whitewashed gypsum. More >