The Archaic or Early Dynastic Period of Egypt is taken to include the First Dynasty and Second Dynasty, lasting from 2920 BC, following the Protodynastic Period, until 2575 BC, or the beginning of the Old Kingdom. Some Egyptologists also include the Third Dynasty. Prior to the unification of Upper and Lower Egypt in circa 3100 BC, the land was settled with autonomous villages. With the first dynasties, the rulers established a national administration and appointed royal governors. The buildings of the central government were typically open-air temples constructed of wood or sandstone.