Teresia, or Thirassia (small tyre), is an island in the Aegean sea, which belongs to the group of Islands of volcanic origin Santorini (Thira) Cyclades. The island is the second largest in the group after Santorini.

In ancient times Teresia was a large part of the island Strongyle, which was an active volcano, known today as Santorini. Approximately 3500 years ago there was a powerful volcanic eruption, which is considered the strongest in the whole history of the Earth. After the explosion, inside a volcanic crater formed a huge hollow space, the walls of which could not withstand its own weight and collapsed, creating thus a huge Caldera. Inside the Caldera gushing waters of the Aegean sea and sank it. Thus was formed the island of Therasia.

Today Teresia - small, intimate island with a length of 5, 7 km, width 2, 7 km and an area of only 9, 3 sq km Highest peak of the island – mountain Viglas, whose height is 295 meters above sea level. The East coast is a steep rock, the Western part is more flat. At Terashi there are three small settlements – Manolos (island capital), Protaras and Agia Irini. According to the 2001 census, the population of the island amounted to 268 people. Administratively Teresia belongs to the municipality of Thira.

Capital Manolos is located on the edge of the Caldera, opposite the island of Santorini and Oia. Small houses, built among the rocks, old windmills, churches and narrow streets create a typical flavor Cycladic village.

It is interesting that on such a small island is a total of 21 churches (including a small chapel, built in the 19th century. The most famous of them - the Church of St. Irene, the Church of St. Constantine, the Church of Panagia Lagadia and the monastery of the Dormition of the virgin.