The earliest known Egyptian pyramids are found at Saqqara, northwest of Memphis. The earliest among these is the Pyramid of Djoser (constructed 2630 BC–2611 BC) which was built during the third dynasty. It started off as a mastaba tomb — a flat-roofed structure with sloping sides — and, through a series of expansions, evolved into a 197-foot-high (60 meters) pyramid, with six layers, one built on top of the other.