When it was built, the Great Pyramid was covered by white stones that formed a smooth outer surface. Some of these stones can still be seen around the base. Most of what can be seen of the pyramid now is its basic core of 2,300,000 blocks of limestone and granite. There have been many different theories to explain how the pyramid was built. Most accepted building ideas are based on the idea of moving huge stones from a quarry and dragging and lifting them into place. Archaeologists found that the Pyramids of Giza were not built by slaves, but workers who were paid for working. Their graves were found near the pyramid in 1990.