The Temple of Poseidon

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.
Source : visitporos.com