According to Greek Mythology, Cape Sounion is the spot where Aegeus, king of Athens, leapt to his death off the cliff, thus giving his name to the Aegean Sea. The story goes that Aegeus, anxiously looking out from Sounion, despaired when he saw a black sail on his son Theseus's ship, returning from Crete. This led him to believe that his son had been killed in his contest with the dreaded Minotaur, a monster that was half man and half bull. The Minotaur was confined by its owner, King Minos of Crete, in a specially designed labyrinth. Every year, according to the myth, the Athenians were forced to send seven men and seven women to Minos as tribute. These youths were placed in the labyrinth to be devoured by the Minotaur. Theseus had volunteered to go with the third tribute and attempt to slay the beast. He had agreed with his father that if he survived the contest, he would hoist a white sail on his return. In fact, Theseus had successfully overcome and slain the Minotaur, but tragically had simply forgotten about the white sail.
The earliest literary reference to Sounion is in Homer's poem the Odyssey, probably composed in the 8th century BC. This recounts the mythical tribulations suffered by Greek hero Odysseus in a gruelling 10-year sea-voyage to return to his native island, Ithaca, in the Ionian Sea, from the sack of Troy. This ordeal was supposedly inflicted upon him by Poseidon, to whom the temple at Sounion was dedicated. The story recounts that as the various Greek commanders sailed back from Troy, the helmsman of the ship of King Menelaus of Sparta died at his post while rounding "holy Sounion, cape of Athens". Menelaus landed at Sounion to give his companion full funeral honours (i.e., cremation on a funeral pyre on the beach). The Greek ships were then caught by a storm off Cape Malea and scattered in all directions.
Archaeological finds on the site date from as early as 700 BC. The 5th-century BC historian Herodotus tells us that in the sixth century BC, the Athenians celebrated a quinquennial 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 BC by Persian troops during Xerxes I's invasion of Greece. 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 captured 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 ca. 440 BC. This was during the ascendancy of the Athenian statesman Pericles, who also rebuilt the Parthenon in Athens.
In 413 BC, during the Peloponnesian War against the Spartans, the Athenians fortified the site with a wall and towers to prevent it 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 Dekeleia, in north Attica. However, not long after, the Sounion fortress was seized from the Athenians by a force of rebel slaves from the nearby silver mines of Laurium.