The Bent Pyramid of Sneferu, Dashur, Egypt

The Bent Pyramid is located at the royal necropolis of Dahshur, 40 kilometres south of Cairo and was built under the Old Kingdom during the reign of the Pharaoh Sneferu (c. 2600 BC).

 A unique example of early pyramid development in Egypt, this was the second pyramid built by Sneferu.
It rises from the desert at a 54-degree inclination, but the top section above 47 metres is built at a shallower angle of 43 degrees, giving the pyramid a visibly 'bent' appearance.
It is believed that the Bent Pyramid represents a transition between the step-sided and smooth-sided pyramids in an attempt to determine the best angle to create the slope of a pyramid. The original steepness of the original angle of inclination began to show signs of instability during construction, forcing the builders to adopt a shallower angle to prevent the structure's collapse.
This appears to be supported by the building of the Red Pyramid, built immediately afterwards by the same pharaoh, which was constructed at the preferred angle of 43 degrees from its base to the top.