The Temple of Poseidon has been dated to around 520 B.C. The peripteral structure was built in the Doric style, with six columns on its narrow sides and twelve on its long sides. It was one of three large sanctuaries dedicated to the sea-god Poseidon in the Saronic area and formed a triangle with the Temple of Aphaia on the island of Aegina and the Temple of Poseidon at Cape Sounio.
Ruins on the sanctuary’s southwest are likely the Kalaureia bouleuterion, or assembly, where representatives of the seven cities participating in its amphictyony net. The ruins southwest of the bouleuterion are believed to have been either a monument dedicated to the orator Demosthenes or the asclepeion, or healing temple. Demosthenes had sought asylum at the sanctuary after fleeing the Macedonians who had seized Athens; he took his own life by swallowing poison and was buried on the sanctuary’s grounds in 322 B.C.