Which sentence describes the Baodun site?

The first prehistoric city site in Chengdu Plain. Because Baodun Site is the earliest site found in the prehistoric city sites in Chengdu Plain, it is also the earliest site found in Chengdu Plain so far, and it is also the only prehistoric city site in China that completely surrounds city walls and trenches. Baodun Site is located in Malong Village, Baodun Town, Xinjin District, Chengdu, Sichuan Province. It is the earliest Neolithic city site found in Chengdu Plain and the birthplace of rice writing in Chengdu Plain, about 4500 years ago.