Pyramids are associated with the ancient Egyptians. The term may also be used to describe any three-dimensional structure whose base is narrower than its height. They are believed to have been built as tombs for pharaohs, although many people believe that pyramids were constructed for astronomical reasons.
The most common type of pyramid shape is a square base leading to a point at the top of the pyramid, which was described by Euclid in 300 BC as being the shape with a triangular base and point on top. The term "pyramid" is derived from the Greek pyramidos meaning "fire".