Sounio cape, the Temple of Poseidon

Cape Sounio has been recognized since prehistoric times as a special place of worship, and was an important sanctuary during the Greek Archaic, Classical, and Hellenistic periods. There are two sanctuaries present on the cape: the sanctuary of Poseidon and the sanctuary of Athena; two gods that were held in high esteem by the ancient Athenians. The ruins as we see them today are the result of the renovations that took place during the 5th century B.C., and replaced a succession of buildings that date back to the archaic period.
The location of cape Sounio at the tip of Attica rendered it as a location of strategic military importance, and thus it was fortified with a mighty wall and guarded constantly by a garrison which ensured that the shipping lanes to Athens remained open. It is also most likely the place that Aegeus plunged to his death after he glimpsed the dark sails of Theseus' ship approaching, thus naming the Aegean Sea after his legend.