The area of Kionia in Tinos is of great historical importance, as here lies the Sanctuary of Poseidon upon the ruins of an ancient temple.

The Sanctuary of Poseidon was Doric. Built in the 4th century BC, it is the only temple in Cyclades which was exclusively dedicated to the god of sea, Poseidon and his wife Amphitrite.

The Sanctuary of Poseidon soon gained nationwide fame and was an important station for pilgrims on their way to Delos island. Poseidon in ancient times was also worshiped as a doctor, while Amphitrite was thought to cure infertile women. So, among the sacred buildings there were some for the religious needs and others operating as hospitals.

During the island's prosperity, the Sanctuary of Poseidon was the main center of worship and a healing center with a great reputation. Also, the "Posidonia" were organized here. These were significant events, including theatrical performances.

The Sanctuary of Poseidon operated until the 3rd century AD. Christianity together with excessive raids, resulted in its abandonment. Astonishingly though, the last stroke was given by the conquerors and the locals who used its materials for the construction of buildings and walls.

Excavations began in the early 20th century, bringing to light the ruins of the sanctuary and other buildings, mosaics and many artifacts, such as statues and a sundial. Many of the findings are exhibited in the Archaeological Museum of Tinos, which is worth visiting before or after your visit to the archaeological site in the Sanctuary of Poseidon.