The three main pyramids at Giza in Egypt were built in the 4th Dynasty around 2550 BC as tombs for kings. The largest and most famous is the Great Pyramid of Khufu, which was the tallest structure in the world for over 4,000 years. The other two major pyramids are those of Khafre and Menkaure, Khafre's being slightly taller than Khufu's due to its location on higher ground.