The fortified outer structures are formed by compacting earth, mixed with stone, granite, bamboo, wood and other readily available materials, to form walls up to 6 feet thick. Branches, strips of wood and bamboo chips are often laid in the wall as additional reinforcement. The entrance is guarded by 4-5 inch thick wooden doors reinforced with an outer shell of iron plate. The top level of these earth building have gun holes.
The tulous are as solid as a castle and offered specular resistance against cannon fire. In 1934, a group of uprising peasants of Yongding County occupied a tulou to resist the assault of the army, which fired 19 cannon shots at that tulou, but made only a small dent on the outside wall.
Housing a whole clan, the whole structure functioned as small village and were known as “a little kingdom for the family” or “bustling small city.” The buildings were divided vertically between families with each disposing of two or three rooms on each floor. In contrast with their plain exterior, the inside of the tulou were built for comfort that is warm in winter and cool in summer, and were often highly decorated. The rooms are well-lit, well-ventilated, windproof, and the entire building earthquake-proof.
There are more than 20,000 tulous in Fujian, scattered in the mountainous southeastern region of Fujian province. Although tulous are found in other parts of China, they are all referred to as Fujian Tulou after UNESCO adopted that name for all dwellings of this type. A total of 46 Fujian Tulou sites have been inscribed in 2008 by UNESCO as World Heritage Site, as "exceptional examples of a building tradition and function exemplifying a particular type of communal living and defensive organization in a harmonious relationship with their environment".