there exist 1,833 diaolous in kaiping's 16 townships. the most typical diaolous are mostly seen in tangkou, baihe, xiangang and chikan township in the central plain. not many can be found in the hilly areas. the five nominated places listed for application for world cultural heritage are located in these four townships. they demonstrate the earliest and most representative diaolous, especially the diaolous built in their most booming time. they are the typical diaolous that combine the chinese and western styles and indicate the relationship with the villages. one can see the various types of diaolous and their different functions, which show their high value. all in all, these diaolous are all major historical and cultural sites to be protected at the national level. the kaiping diaolou mainly served the purposes of defence and dwelling. kaiping diaolou is divided into three types: night watchtowers, communal towers and dwelling towers. the night watchtowers were built for joint defence among villages. they were mostly built at the entrance of the villages, on the hill or beside the river outside the village. they functioned to give alarm. the communal towers were built in the rear part with the funds raised by all villagers or many households. each family had one room to hide themselves in case of bandits' attack. such towers were built in a sealed and simple way for the purpose of defence. solely rich families built the dwelling towers at the back of the village. such towers well combine the two purposes. high, spacious and nice-looking as well as convenient for living, they are usually the symbols of a village. the upper part of the diaolous is built in the form of colonnade, terrace, receding terrace, over-hanging, castle and mixture of different styles. the appearance of a diaolous reflects the economic strength of the owner, aesthetic taste and the impact of external culture. this is the most interesting part of the diaolous. from building materials and structure, kaiping diaolous can be divided into stone towers, lime-sand-clay towers, brick towers (including brick-wood and brick-concrete structure) and steel reinforced concrete towers. the stone and brick towers were mainly built in the hilly areas. they had a longer history. the early brick towers were of brick-wood structure. later, they were mostly of brick-concrete structure. the steel reinforced concrete buildings were mostly seen in the plain areas. in the early 20th century, much steel and cement started to be used. local people then began to accept modern building materials and technology.