The largest of the three pyramids at Giza, known as the Great Pyramid, is truly an astonishing work of engineering. It was built over a twenty year period. Some believe that it was built by slaves, but this is not true. One hundred thousand people worked on the great structure for three months of each year, during the Nile’s annual flood when it was impossible to farm the land and most of the population was unemployed. The pharaoh provided good food and clothing for his workers, and was kindly remembered in folk tales for many centuries. The sides are oriented to the four cardinal points of the compass and the length of each side at the base is 755 feet (230.4 m). The faces rise at an angle of 51º 52’ and their original height was 481 feet (147 m). (They currently rise 451 feet [138 m].) It was constructed using around 2,300,000 limestone blocks, each weighing an average of 2.5 tons. Some blocks weigh as much as 16 tons. For centuries, the Great Pyramid was encased in smooth limestone, but this was plundered in our era to build Cairo. Khafre 2558–2532 BC Giza7Khufu’s son, Khafre (also known as Chephren). His pyramid, on a nearby site at Giza, appears taller than his father’s, but this is an illu¬sion; it is built on higher ground and was in fact, origi¬nally at 447 .5 feet (136.4 m), 33.5 feet (10.2 m) shorter than the Great Pyramid.Khafre’s pyramid retains some of its original limestone casing at the apex, and so it is possible to imagine how the pyramids might have ap¬peared in antiquity. Khafre also built the Great Sphinx, which is 66 feet high (20 m) and 240 feet long (73 m) and is part of Khafre’s pyramid complex. It represents Ra-Harakhte, the sun god, as he rises in the east at dawn but the face of the Sphinx is a portrait of Khafre himself, and is contemporary with his pyramid. It was carved from an outcropping of limestone left after quarrying the stone for his father’s pyramid Unfortunately, the great sphinx has deteriorated over the millennia and was extensively renovated in ancient times. More recently it was mutilated by the Sultan Mohammed an-Nasir in AD 1300; and lost its nose in 1798, when Napoleon’s soldiers used it for target practice.There have recently been a number of speculative theories concerning the age of the Great Sphinx, but no material evidence exists to suggest that its history should be revised.