The Bent Pyramid was originally planned as a true pyramid, but the corners were built on unstable ground and the walls of the burial chambers inside began to crack and shift inward. Of necessity, the building’s geometry was altered at a point just above half its height. The angle of incline was decreased from 54º 31’ 13’’ to 43º 21’. This was probably done to alleviate the stresses in the lower part of the pyramid and make it stronger. But the bent pyramid was never used. Instead, Sneferu began a third pyramid about a mile way. This one is called the red pyramid because of the red limestone blocks used in its construction. It became the world’s first successful true pyramid.