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A pyramid is any three-dimensional polyhedron where the faces other than the base are triangular and converge on one point, called the apex.
The base of a pyramid can be any polygon but is typically a square, leading to four non-base faces. - from Wikipedia.
The most famous pyramids are the ones found in Egypt.
There are three pyramids in Giza - there is the Khufu's Pyramid, Khafre's Pyramid and Menkaure Pyramid.
Khufu's Pyramid, is the oldest and largest of the three pyramids bordering what is now Cairo, Egypt and is the only remaining member of the Seven Wonders of the Ancient World. It is
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Khafre's Pyramid, is the second largest and the tomb of Pharoah Khafre. The pyramid has a base length of 215.25 m (707 ft) and originally rises to a height of 143.5 m (471 ft) The Pyramid is made of Limestone blocks(weighing more than 2 tons each). - from Wikipedia
Menkaure's Pyramid, is the smallest among the three pyramids and the tomb of Egyptian Pharaoh Menkaure. It was probably completed that time between the 26th century BC.
I wasn't expecting to be THERE - for real - but there I am standing right in front on one of the Ancient Seven Wonders of the World and the only surviving structure in modern times. Woot.