Poseidonia is a village and a former municipality

Communities and Municipalities of Greece

For the new municipalities of Greece see the Kallikratis ProgrammeThe municipalities and communities of Greece are one of several levels of government within the organizational structure of that country. Thirteen regions called peripheries form the largest unit of government beneath the State. ...

 on the island of Syros

Syros

Syros , or Siros or Syra is a Greek island in the Cyclades, in the Aegean Sea. It is located south-east of Athens. The area of the island is . The largest towns are Ermoupoli, Ano Syros, and Vari. Ermoupoli is the capital of the island and the Cyclades...

, in the Cyclades

Cyclades

The Cyclades is a Greek island group in the Aegean Sea, south-east of the mainland of Greece; and a former administrative prefecture of Greece. They are one of the island groups which constitute the Aegean archipelago. The name refers to the islands around the sacred island of Delos...

, Greece

Greece

Greece , officially the Hellenic Republic , and historically Hellas or the Republic of Greece in English, is a country in southeastern Europe....

. Since the 2011 local government reform it is part of the municipality Syros-Ermoupoli

Syros

Syros , or Siros or Syra is a Greek island in the Cyclades, in the Aegean Sea. It is located south-east of Athens. The area of the island is . The largest towns are Ermoupoli, Ano Syros, and Vari. Ermoupoli is the capital of the island and the Cyclades...

, of which it is a municipal unit. The population was 3,006 inhabitants at the 2001 census, and the land area is 23.705 km². The municipal unit shares the island of Syros with the municipal units of Ano Syros

Ano Syros

Ano Syros is a town and a former municipality on the island of Syros, in the Cyclades, Greece. Since the 2011 local government reform it is part of the municipality Syros-Ermoupoli, of which it is a municipal unit. The municipal unit includes the uninhabited islands Gyaros and Varvaroúsa....

 and Ermoupoli

Ermoupoli

Ermoupoli , also known by the formal older name Ermoupolis or Hermoupolis , is a town and former municipality on the island of Syros, in the Cyclades, Greece. Since the 2011 local government reform it is part of the municipality Syros-Ermoupoli, of which it is the seat and a municipal unit...

. Also known as Dellagrazia (name taken from a small church Maria Della Grazia).