The pyramids are huge: the largest one is the Great Pyramid of the pharaoh Khufu. It contains 2.5 million stone blocks, weighs over six million tons, and is as tall as a 40-story skyscraper.

People used to think that the pyramids were built by slaves. They didn't think that thousands of people could have been organized to work on such big projects without someone forcing them to do it. After studying more ancient Egyptian records, historians—people who study things that have happened in the past—believe that free Egyptians, not slaves, built the pyramids.