The Great Pyramid of Giza is the largest Egyptian pyramid and served as the tomb of pharaoh Khufu, who ruled during the Fourth Dynasty of the Old Kingdom. Built in the early 26th century BC, over a period of about 27 years, the pyramid is the oldest of the Seven Wonders of the Ancient World, and the only wonder that has remained largely intact. It is the most famous monument of the Giza pyramid complex, which is part of the UNESCO World Heritage Site "Memphis and its Necropolis". It is situated at the northern end of the line of the three pyramids at Giza. Initially standing at 146.6 meters (481 feet), the Great Pyramid was the world's tallest human-made structure for more than 3,800 years. Over time, most of the smooth white limestone casing was removed, which lowered the pyramid's height to the current 138.5 meters (454.4 ft); what is seen today is the underlying core structure. The base was measured to be about 230.3 meters (755.6 ft) square.