The Parthenon is a Doric peripteral temple, which means that it consists of a rectangular floor plan with a series of low steps on every side, and a colonnade of Doric columns extending around the periphery of the entire structure. Each entrance has an additional six columns in front of it. It was built to replace two earlier temples of Athena on the Acropolis. One of these, of which almost no trace remains today, stood south of the Parthenon (between the Parthenon and the Erechtheum). The other, which was still being built at the time of the Persian sack in 480, was on the same spot as the Parthenon. We know the names of the architects (Iktinos and Kallikrates) and also of the sculptor (Pheidias) who made the massive chryselephantine cult statue of the goddess.