History

According to the ancient travel - writer Pausania...

Poseidon's Temple
... Poros is comprised of two islands Sphairia and Kalavria
(the name Kalavria means "gentle Breeze"). Kalavria at first was offered
to the god Apollo and he made it over to the god Poseidon in return
for Delphi. Kalavria is quite larger than Sphairia and is planted all over. Sphairia is a volcanic rock.

In mythology times Aithra founded in Sphairia the temple of Athena Apatoria in honor of her encounter with the god Poseidon.

In the north part of the island there are the ruins of Poseidon's Temple, which was built in 520BC. The main Temple was built in Doric style, though some of its columns were Ionian. Nearly the Temple there was the built up area of Kalavria.

Such was the place's importance
that it functioned as the center
for the Amphictyonic League (amphictionnes: dwellers around")
a voluntary "cooperative"
of city-states in both civic and religious matters, which included Hermione, Epidauros, Aigina, Prassies, Athens and Orhomenos.
At the Poseidon's Temple came Demosthenes the ancient great orator availing himself of its right
of sanctuary as Philip
the King of Macedonia chased him.

Poseidon's Temple

1821
Poros played a significant
role in 1821 Revolution.
It was placed on the map
of history in 1828 where rival assemblies met to make
important decisions,
which set the Constitution
in a positive direction.
In 1830 the building of
the shipyard and naval station
at Poros began.
The arson of the armada