It has variously been claimed that the pyramids served as power plants, water pumps, astronomical observatories, sources of ill-defined pyramid- power energy vortices, guidance beacons for alien spacecraft sites for mystery initiation ceremonies.
Unfortunately there remains no known written record as to how the most famous of the more than 100 pyramids in Egypt, the Great Pyramid of Giza, was built, nor have any reliefs depicting the building ever been found. The Greek geographer Herodotus, writing in the fifth century BC, mentioned the theory that levers were used to lift pyramid stones. Perhaps this is the most tenable of the alternate theories; as reported by Egyptologist Selim Hassan in his opus Ancient Egypt, Part 1, Cairo, 2000, p. 288. Hassan verified Herodotus's theory based on excavation conducted by Cairo University in the mid-20th century on the Giza Plateau, where the debris of two pulleys were found, one near the second pyramid and one inside the workmen's village east of the valley.
Mostly a summary article on various pyramid theories.