This temple, made of pentelic marble, is about 23 feet high, 27 feet long, and 18 feet wide. The columns are 13 feet high, and the ratio of height to its diameter is 7:1. The temple faces east, with its back side facing the entrance of the acropolis. Around 410 B.C., a parapet was constructed around the temple (except the east), to protect the visitors from falling off the bastion.