section_path: Pyramidion and missing tip
section_name: Pyramidion and missing tip
paragraph_text: Pyramidion and missing tip
  
  The pyramid was once topped by a capstone known as a pyramidion. The material from which it was made is subject to much speculation; limestone, granite or basalt are commonly proposed, while in popular culture it is often solid gold, gilded or electrum. All known 4th dynasty pyramidia (of the Red Pyramid, Satellite Pyramid of Khufu (G1-d) and Queen's Pyramid of Menkaure (G3-a)) are of white limestone and were not gilded. Only from the 5th dynasty onward is there evidence of gilded capstones; for instance, a scene on the causeway of Sahure speaks of the "white gold pyramidion of the pyramid Sahure's Soul Shines".
  
  The Great Pyramid's pyramidion was already lost in classical antiquity, as Pliny the Elder and later authors report a platform on its summit. Over time more stones were removed from the peak, and nowadays the pyramid is about 8 metres (26 ft) shorter than it was when intact, with about 1,000 tonnes (2,200,000 lb) of material missing from the top.
  
  In 1874 a mast was installed on the top by the Scottish astronomer David Gill who, whilst returning from work involving observing a rare Venus transit, was invited to survey Egypt and began by surveying the Great Pyramid. His measurements of the pyramid were accurate to within 1 mm, and the survey mast is still in place to this day.