Very little has survived of ancient Chinese architecture, due to the extensive use of timber as a building material. Brick and stone vaults used in tomb construction have survived, and the corbeled dome was used, rarely, in tombs and temples. The earliest true domes found in Chinese tombs were shallow cloister vaults, called "simian jieding", derived from the Han use of barrel vaulting. Unlike the cloister vaults of western Europe, the corners are rounded off as they rise. The first known example is a brick tomb dating from the end of the Western Han period, near the modern city of Xiangcheng in Henan Province. These four-sided domes used small interlocking bricks and enabled a square space near the entrance of a tomb large enough for several people that may have been used for funeral ceremonies. The interlocking brick technique was rapidly adopted and four-sided domes became widespread outside Henan by the end of the first century AD.