Any line of rulers whose right to power is inherited; usually a line of kings, related by blood, who succeed each other on a throne. Egyptian history was divided into 31 dynasties by Manetho in the 3rd century BC when he wrote a history of Egypt. The dynasties of Mesopotamia were distinguished by their places of origin rather than their relationships, e.g. those of Ur, Larsa, etc. In China the dynasties were longer-lived and often encompassed only regions, those of Shang and Chou spanning twelve centuries. The term is sometimes used for rulers from a single city or ethnic group.