It is thought, from New Kingdom graffitti, that the pyramid was constructed by Sneferu of the Fourth Dynasty. Its core is in the form of a step pyramid, which was later converted to a true pyramid by filling in the steps with limestone encasing. The Meidum pyramid was built in different stages, beginning as a seven-step pyramid to which an additional step was added at a later stage. It appears to have collapsed sometime during the New Kingdom.
Meidum in Digital Egypt