It took the ancient Egyptians around 400 years to progress from mud brick Mastaba to smooth-sided pyramids. The last stage, from stepped to "true" or smooth sided pyramid took only 65 years. The Bent Pyramid (above) is considered to be Egypt's first proper pyramid because until this time pyramids were stepped (see Saqqara). The prevailing theory is that the pyramid is bent because once it began to rise the whole structure became unstable and so it had to be completed at a shallower slope. Unusually for pyramids dating from this period, much of its outer limestone casing is till intact,, giving a good impression of what a visually stunning sight it must once have been.
Left you can see the runes of one of the older mud pyramids.