The dramatic coastal location of Soúnio (Cape Sounion), 5.5 miles south of Athens, was an ideal spot for a Temple of Poseidon, god of the sea. Standing atop sheer cliffs that tumble into the Aegean Sea, the gleaming marble of the Temple of Poseidon has been a landmark for mariners from ancient times to today.
Soúnio has been a sacred site since very ancient times. The “sanctuary of Sounion” is first mentioned in the Odyssey, as the place where Menelaus stopped during his return from Troy to bury his helmsman, Phrontes Onetorides.
Archaeological evidence has shown that there were two organized places of worship on the cape by the 7th century BC: a sanctuary of Poseidon at the southern edge and a sanctuary of Athena about 500 m to the northeast.
Construction on a grand Temple of Poseidon began around 500 BC but was never completed; the temple and all the votive offerings were destroyed by the Persians in 480 BC. The Temple of Poseidon that now stands at Soúnio was built in 444 BC atop the older temple ruins. The Temple of Athena was also built at this time, atop her ancient sanctuary on the cape.
The sanctuaries began to decline from the 1st century BC onwards. Pausanias, who sailed along the coast around 150 AD, wrongly believed the prominent temple on the hill was the Temple of Athena.
Modern travellers visited Sounion long before excavations started on the site, including Lord Byron in 1810. Systematic excavations began on the site in 1897 and continue today. (Stolen from the web)