An illustration of two pyramids. A pyramid is a building where the upper surfaces are triangular and converge on one point. The base of pyramids are usually quadrilateral or trilateral (but generally may be of any polygon shape), meaning that a pyramid usually has three or four sides. A pyramid's design, with the majority of the weight closer to the ground, means that less material higher up on the pyramid will be pushing down from above.
William Swinton Outlines of the Worlds History, Ancient Mediabal and Mondern, with special relation to the history of civilization and the progress of mankind (New York, NY: Ivison, Blakeman and Company, 1874)
Courtesy the private collection of Roy Winkelman