On the edges of Cairo, Egypt lie the three ancient Pyramids of Giza. The largest of the three, the Great Pyramid of Giza (also known as the Pyramid of Khufu, or Pyramid of Cheops) is the only surviving monument of the Seven Wonders of the Ancient World. For over 3,800 years the Great Pyramid of Giza was the tallest structure in the world. It was built over a period of 20 years starting in 2551 BCE from over 2.3 million limestone blocks, and its original purpose was to be the tomb of Egyptian pharaoh Khufu. The two smaller pyramids are the Pyramid of Khafre (or Chephren), and the Pyramid of Menkaure. The alignment of the three pyramids is very similar to that of the constellation Orion. The Great Sphinx is also nearby. Visitors to the pyramids can choose from a variety of accommodations in Cairo.