A pyramid is a structure whose outer surfaces are triangular and converge at a single point. The base of a pyramid can be trilateral, quadrilateral, or any polygon shape, meaning that a pyramid has at least three triangular surfaces (at least four faces including the base). The square pyramid, with square base and four triangular outer surfaces, is a common version. A pyramid's design, with the majority of the weight closer to the ground, and with the pyramidion on top means that less material higher up on the pyramid will be pushing down from above. This distribution of weight allowed early civilizations to create stable monumental structures. For thousands of years, the largest structures on Earth were pyramids—first the Red Pyramid in the Dashur Necropolis and then the Great Pyramid of Khufu, both of Egypt, the latter the only one of the Seven Wonders of the Ancient World still remaining. Khufu's Pyramid is built entirely of limestone, and is considered an architectural masterpiece. The largest pyramid by volume is the Great Pyramid of Cholula, in the Mexican state of Puebla.