Hakka Fortified Villages
As mentioned on p19 of the rule book, the Hakka (Kèjiā 客家) live in fortified villages in the hilly areas of South China.
These walled villages are built to be easily defensible. Each village is made up of about half a dozen round or square fortified houses, called tǔlóu 土楼 ("earthen structures"). Each tǔlóu houses several related families and is internally divided into many compartments for food storage, living quarters, ancestral temple, armoury, etc.
The individual family quarters are built within the walls of the tǔlóu, whereas the common buildings are in the centre of the structure. Each tǔlóu has but a single heavy gate to communicate with the outside world.