Pyramid at Abu Sir
There are a total of seven pyramids at this site, which served as the main royal necropolis during the Fifth Dynasty. The quality of construction of the Abu Sir pyramids is inferior to those of the Fourth Dynasty — perhaps signalling a decrease in royal power or a less vibrant economy. They are smaller than their predecessors, and are built of low quality local limestone.
The three major pyramids are those of Niuserre (which is also the most intact), Neferirkare Kakai and Sahure. The site is also home to the incomplete Pyramid of Neferefre. All of the major pyramids at Abu Sir were built as step pyramids, although the largest of them — the Pyramid of Neferirkare Kakai — is believed to have originally been built as a step pyramid some seventy metres in height and then later transformed into a “true” pyramid by having its steps filled in with loose masonry.
Source: http://en.wikipedia.org/wiki/Egyptian_pyramids