The pyramid of Khafre or of Chephren (, ) is the middle of the three Ancient Egyptian Pyramids of Giza, the second tallest and second largest of the group. It is the tomb of the Fourth-Dynasty pharaoh Khafre (Chefren), who ruled . Size The pyramid has a base length of 215.5 m (706 ft) and rises up to a height of . It is made of limestone blocks weighing more than 2 tons each. The slope of the pyramid rises at a 53° 13' angle, steeper than its neighbor, the pyramid of Khufu, which has an angle of 51°50'24". Khafre's pyramid sits on bedrock 10 m (33 ft) higher than Khufu's pyramid, which makes it appear to be taller. History The pyramid was likely opened and robbed during the First Intermediate Period. During the Nineteenth Dynasty, the overseer of temple construction took casing stones to build a temple in Heliopolis on Ramesses II's orders. Arab historian Ibn Abd al-Salam recorded that the pyramid was opened in 1372 AD. On the wall of the burial chamber, there is an Arabic graffito that probably dates from the same time. It is not known when the rest of the casing stones were robbed; they were presumably still in place by 1646, when John Greaves, professor of Astronomy at the University of Oxford in his Pyramidographia, wrote that, while its stones were not as large or as regularly laid as in Khufu's, the surface was smooth and even free of breaches or inequalities, except on the south. The pyramid was first explored in modern times by Giovanni Belzoni on March 2, 1818, when the original entrance was found on the north side. Belzoni had hopes of finding an intact burial but the chamber was empty except for an open sarcophagus and its broken lid on the floor. The first complete exploration was conducted by John Perring in 1837. In 1853, Auguste Mariette partially excavated Khafre's valley temple, and, in 1858, while completing its clearance, he managed to discover a diorite statue of Khafre. Construction Like the Great Pyramid, a rock outcropping was used in the core. Due to the slope of the plateau, the northwest corner was cut 10 m (33 ft) out of the rock subsoil, and the southeast corner was built up. The pyramid is built of horizontal courses. The stones used at the bottom are very large, but as the pyramid