In the archaic period, the first temple at Olympia was built to Hera (see upper left, Heraion). Beyond it are several old altars and a Metroön (temple of Rhea/Kybele, Mother of the Gods). Another old shrine embedded in the hillside was for Eileithyia, goddess of birth, and Sosipolis, a snake god. Only the priestess and an old woman guardian could enter the inner sanctuary of the snake. Women sang hymns and burned incense in the outer shrine. The temple of Zeus was built centuries later, and the treasuries even later. From Jane Harrison's Prolegomena to the Study of Greek Religion.