There are over 4,000 earth buildings in Yongding County, structurally either square or round. According to ancient Chinese philosophy, heaven is round and earth is square. Thus, varieties of square and circular earth buildings cluster in the mountainous areas. With a thickness of 20 to 30cm, the wooden-board gate lies on the building exterior with an iron sheet. A window on the wall allows for ventilation and sunlight, as well as provides enemy surveillance. Yong Ding Hakka Earth Buildings are not only fire-proof, but can also keep out wild animals. Among all the earth buildings, Zhencheng Building is the most magnificent; Yijing Building is the tallest while Huanji Building is the most mysterious.