A pyramid is any three-dimensional structure 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 four or five sides. The measurements of these triangles uniformly classify the shape as isosceles and sometimes equilateral.
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. This 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, the only remaining Wonder of the World. The largest pyramid ever built, by volume, is the Great Pyramid of Cholula, in the Mexican state of Puebla. This pyramid is considered the largest monument ever constructed anywhere in the world, and is still being excavated. Although the name pyramid is used across the world to describe ancient structures convention dictates that naming them such is not really correct. Technically a true pyramid has four smooth sides and the only ones that exist are those in Egypt and various other areas around the world which were based on the Egyptian model.