File:Temple of Poseidon - Western fascade.jpg

English: Archaeological finds on the site date from as early as 700 B.C. Herodotus tells us that in the sixth century B.C., the Athenians celebrated a quadrennial festival at Sounion, which involved Athens' leaders sailing to the cape in a sacred boat. The original, Archaic Period temple of Poseidon on the site, which was built of tufa, was probably destroyed in 480 B.C. by Persian troops during shahanshah Xerxes I 's invasion of Greece (the second Greco-Persian War). Although there is no direct evidence for Sounion, Xerxes certainly had the temple of Athena, and everything else, on the Acropolis of Athens razed as punishment for the Athenians' defiance. After they defeated Xerxes in the naval Battle of Salamis, the Athenians placed an entire enemy trireme (warship with three banks of oars) at Sounion as a trophy dedicated to Poseidon.

The later temple at Sounion, whose columns still stand today, was probably built in c.440 B.C. This was during the ascendancy of Athenian statesman Pericles, who also rebuilt the Parthenon in Athens. In 413 B.C., during the Peloponnesian War against the Spartans, the Athenians fortified the site with a wall and towers, to prevent the site from falling into Spartan hands. This would have threatened Athens' seaborne grain supply route from Euboea. Athens' supply situation had become critical, since the city's land supply - lines had been cut by the Spartan fortification of Deceleia, in north Attica. However, not long after, the Sounion fortress was seized from the Athenians by a force of fugitive slaves from the nearby silver mines of Laurium.

The earliest literary reference to Sounion is in Homer 's poem the Odyssey, probably composed in the 8th century B.C. This recounts the mythical tribulations suffered by Greek hero Odysseus in a gruelling 10-year sea-voyage to return to his native island, Ithaca, from the sack of Troy. This ordeal was supposedly inflicted upon him by Poseidon, to whom the temple at Sounion was dedicated. The sea-god was enraged that Odysseus had slain Poseidon's son the Cyclops (one-eyed giant) Polyphemus. (The fact that Odysseus was forced to do this to avoid being eaten by Polyphemus evidently was not considered a mitigating factor by Poseidon). We are told that, as the various Greek commanders sailed back from Troy, the helmsman of King Menelaos of Sparta 's ship died at his post while rounding "holy Sounion, cape of Athens". Menelaos landed at Sounion to give his companion full funeral honours. The Greek ships were then caught by a storm off Cape Malea and scattered. It was this storm that drove Odysseus' ship to the land of the lotus-eaters (believed to be an island off the north African coast). From there he sailed to the land of the Cyclops, where he and his men were taken prisoner by Polyphemus.