From MSNBC:
A French architect says he has cracked a 4,500-year-old mystery surrounding Egypt’s Great Pyramid, claiming that it was built from the inside out. Scientists have long wondered how the Egyptians placed the Great Pyramid’s 3 million stone blocks, which each weigh about 2.5 tons. Previous theories have suggested that the tomb of Pharaoh Cheops (Khufu), the last surviving example of the seven great wonders of antiquity, was built using either a vast frontal ramp or a ramp in a corkscrew shape around the exterior to haul up the stonework.
But flouting previous wisdom, Jean-Pierre Houdin said advanced 3-D technology has shown that the main ramp used to haul the massive stones to the apex was contained 30 to 50 feet (10 to 15 meters) beneath the outer skin, tracing a pyramid within a pyramid. According to his theory — shown in a computer model — the builders put up an outer ramp for the first 140 feet (40 meters), then constructed an inner ramp in a corkscrew shape to complete the 450-foot-high (137-meter-high) structure.
More here.