The Great Pyramid of Giza was built by the ancient Egyptians during the reign of Pharaoh Khufu in the 4th dynasty of the Old Kingdom. It is estimated to have been constructed over a 20-year period between 2550 and 2490 BCE. The Great Pyramid is the oldest and largest of the three pyramids in the Giza Necropolis and is believed to have been built as a tomb for Pharaoh Khufu.