The Yuchang Building, the oldest surviving tulou in China. Tulou are fortified, adobe (earth) Hakka clan houses, many of them circular like this one, 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. This building, in Xiabang Village, Shuyang Town, Nanjing County, was built 1308-1338, has 5 stories and 270 rooms, with an ancetral hall in the centre.