"The pyramid at Meidum is thought to have been originally built for Huni, the last pharaoh of the Third Dynasty. It was completed and probably usurped by his successor, Sneferu, who also turned it from a step pyramid into the first true pyramid by filling in the steps with limestone encasing. It appears to have collapsed sometime during the New Kingdom, and is sometimes known as the Collapsed Pyramid or the Failed Pyramid. Its final dimensions were first meausred my Petrie in the 1890s"

Thanks.
Dave Light.