When it was built, the Great pyramid was 145.75 m (481 ft) high. Over the years, it lost 10 m (30 ft) off its top. It ranked as the tallest structure on Earth for more than 43 centuries, only to be surpassed in height in the nineteenth century AD. It was covered with a casing of stones to smooth its surface (some of the casing can still be seen near the top of Khefre's pyramid). The sloping angle of its sides is 51 degrees and 51 minutes. Each side is carefully oriented with one of the cardinal points of the compass, that is, north, south, east, and west. The horizontal cross section of the pyramid is square at any level, with each side measuring 229 m (751 ft) in length. The maximum error between side lengths is astonishingly less than 0.1%. The structure consists of approximately 2 million blocks of stone, each weighing more than two tons. It has been suggested that there are enough blocks in the three pyramids to build a 3 m (10 ft) high, 0.3 m (1 ft) thick wall around France. The area covered by the Great pyramid can accommodate St Peter's in Rome, the cathedrals of Florence and Milan, and Westminster and St Paul's in London combined. On the north face, is the pyramid's entrance. A number of corridors, galleries, and escape shafts either lead to the King's burial chamber, or were intended to serve other functions. The King's chamber is located at the heart of the pyramid, only accessible through the Great Gallery and an ascending corridor. The King's sarcophagus is made of red granite, as are the interior walls of the King's Chamber. Most impressive is the sharp-edged stone over the doorway which is over 3 m (10 ft) long, 2.4 m (8 feet) high and 1.3 m (4 ft) thick. All of the interior stones fit so well, a card won't fit between them. The sarcophagus is oriented in accordance with the compass directions, and is only about 1 cm smaller in dimensions than the chamber entrance. It might have been introduced as the structure was progressing. New theories concerning the origin and purpose of the Pyramids of Giza have been proposed... Astronomic observatories... Places of cult worship... Geometric structures constructed by a long-gone civilization... Even extraterrestrial-related theories have been proposed with little evidence in support... The overwhelming scientific and historic evidence still supports the conclusion that, like many smaller pyramids in the region, the Great Pyramids were built by the great Ancient Egyptian civilization off the West bank of the Nile as tombs for their magnificent Kings... Tombs where Khufu, Khefre, and Menkaure could start their mystic journey to the afterlife.
excerpt from the text of Alaa K. Ashmawy