Sounion was fortified in the nineteenth year of the Peloponnesian War (413 BCE) for the purpose of protecting the passage of the cornships to Athens, and was regarded from that time as one of the principal fortreses of Attica. Its proximity to the silver mines of Laurium probably contributed to its prosperity, which passed into a proverb; but even in the time of Cicero it had sunk into decay. The circuit of the walls may still be traced, except where the precipitous nature of the rocks afforded a natural defence. The walls which are fortified with square towers, are of the most regular Hellenic masonry, and enclose a space or a little more than half a mile in circumference. The southern part of Attica, extending northwards from the promontory of Sounion as far as Thoricus on the east, and Anaphlystus on the west, is called by Herodotus the Suniac angle (τὸν γουνὸν τὸν Σουνιακόν). Though Sounion was especially sacred to Athena, we learn from Aristophanes that Poseidon was also worshipped there.