A rectangular 'tulou' near Chuxi town in Fujian Province, southern China. Tulou are fortified, adobe (earth) Hakka clan houses, many of them circular like this, found only in the hills of Fujian Province in southern China. This unique architecture evolved as a means of defence when the Hakka migrated to this region beginning in the 13th century. A few thousand tulou remain today in use, of which perhaps one thousand are round, known as yuanlou.