The first Egyptian pyramid was built over 4,500 years ago as a burial monument for an Egyptian pharaoh, the then ruler of ancient Egypt. His successors followed this burial tradition, and like their predecessors, they were mummified after death and placed inside a pyramid, along with valuables and personal belongings. A total of approximately eighty pyramids have been preserved, built over a period of about a thousand years. The earliest form of a pyramid is the mastaba, a box-shaped structure in which important figures were buried. The step pyramid of Pharaoh Djoser at Saqqara represents the first step toward the construction of true pyramids. The shape of the pyramids likely had two meanings: 1. Primordial mound: according to one cosmogony, the primordial mound, or tumulus, was the first thing to emerge from chaos/water. The primordial mound represented creation, and the pyramid symbolised the creation of rebirth after death. 2. Heavenly Staircase: a 'stairway to heaven': the pharaoh used the pyramid as a staircase to ascend among the circumpolar stars after his death. Archaeological research has shown that various elements in the architectural style and positioning of the pyramids are related to the worship of the gods of the time (the sun god) and that the position of the celestial bodies was taken into account. This theory, however, is controversial and is considered pyramidology by Egyptologists.