It is located almost at the center of the island and myth has it that Poseidon exchanged his Temple at Delphi with the one that Apollon had at Kalavria in Poros. The Temple of Poseidon is of the Dorian order and it has six columns on its short side and 12 columns on its long side (27.40 X14.40). The exact date that it was built is uncertain. The year 520 BC is claimed by N. Faraklas, although I. Stamatiou claims that it was built around the 6th century BC, and still others claim that it was built much earlier.
According to Giannis Poulakis in his book, Poros and Its History (p. 43) "The Temple of Poseidon soon developed into a prestigious and Panhellenic place of worship and became a center where many Hellenic cities founded the first and most powerful in the Hellenic world amphictyony*".
The amphictyony of Kalavria consisted of seven cities. After the dissolution of the amphictyony which is estimated to have occurred around the 5th century BC, the Temple of Poseidon continued to be a place of worship.
Although the Temple of Poseidon, the statues that it once had have been pillaged. For example what remains of Poseidon's statue (estimated to be about 5 meters in height) is the foot of the statue (about 70 centimeters long), which is stored in the Poros Museum.
* In short, amphictyony is a political and cultural association among cities with a common Temple of worship.