The Castle of Agioi Theodoroi, known today as Evraiokastro or Ovriokastro or Vriokastro, is located in the northwestern coastal part of the island, east of Gavathas and more specifically at the northern end of a small peninsula, which, together with the adjacent rocky Acropolis to the south, formed the main area where the ancient city of Antissa, one of the six most important city-states of Lesbos in antiquity, was founded and flourished from the end of the second millennium. onwards. According to legend, the head and lyre of Orpheus, the mythical poet and musician of antiquity, who was dismembered and thrown into the sea of Evros by the Maenads of Thrace, ended up in Antissa. To the west of the city, there was the fertile valley by Voulgaris river and to the east, the ancient harbour, from which parts of the engulfed in water jetty and few building remains of the fortification are preserved to this day. The necropolis of ancient Antissa extended to the south and southwest.

The German architect and archaeologist Robert Johann Koldewey (1855-1925) was the first to locate, identify and map the ancient city of Antissa, which, as is shown in the relevant topographic maps, was surrounded by walls built according to the masonry system of Lesbos. It is assumed that it occupied a total of 165 hectares, while the perimeter of its walls was approximately 2 km. The important data provided by Koldewey were largely confirmed by the findings of the excavations carried out by the British archaeologist and historian Winifred Lamb (1894-1963) between 1930 and 1932. Apart from fragmentarily preserved parts of the walls, the building remains and the wells, the archaeological excavation brought to light a wealth of portable finds, such as pottery, inscriptions, coins and figurines, covering a wide chronological range from the end of the 2nd millenn. BC to the 16th c. AD, which attest to the continuous and uninterrupted occupation of the site. The most important archaeological finds include the building remains of an early sanctuary, which seems to have been founded around 1000 BC. It is an arched, four-part cult building from which at least two building phases can be distinguished, with the second one dating back to the 8th c. BC, when the cult building was transformed into an ellipsoidal building, acquiring a double arch at its narrow ends. An elongated, rectangular building of the 4th c. BC which is associated with a stoa, seems to be related to the wider sanctuary area.

In 167 BC, ancient Antissa was destroyed by the Romans. In the years that followed, the medieval settlement of Agioi Theodoroi developed in the area and during the Byzantine period took the form of an important walled town, protected by its homonymous fortified Castle. Ovriokastro was drastically reinforced by the Gattilusi during their rule of Lesbos (1355-1462). After the conquest of the island by the Ottomans in 1462, and more specifically at the end of the First Ottoman-Venetian War (1461-1479), it was abandoned and destroyed. The Castle of Agioi Theodoroi, also called ‘Tsifút Kalesi’ by the Ottomans, was one of the three largest and most important medieval Castles on the island of Lesbos, after those of Mytilene and Mithymna.

Today, it is preserved in a ruined state and is located at the northern end of a peninsula, which itself provided natural fortification to the area on a large degree, especially at its northern rocky and steep end. The south-facing, lower-lying and relatively flat part of its narrow ridge was reinforced by a high wall with a gate, bastions, towers and a fortified moat along its entire length. A circular tower at its southeastern end (probably a later addition) provided further reinforcement and protection for the harbour of the town on the east. The walls of the Castle, which exceeded 20 m. in height in several places, pentagonally enclosed the perimeter of the peninsula in its entirety, providing the required fortification and protection to the walled town. At the northern end was the Upper Castle, the last line of defence for its defenders, reinforced in the southern part by five fortified towers. Today, most of the walls of Ovriokastro have not survived. In the interior, the remains of residential buildings and other buildings of various uses, which were intended for the officials and the garrison, are preserved.

In a patriarchal synodal decision of 1331, it is mentioned that in the fortified town of Agioi Theodoroi, there was a monastery dedicated to the Virgin Mary The Guide. In 1334, the Castle was occupied by the Genoese pirate Dom. Cattaneo, and in 1462, it fell into the hands of the Ottomans, along with the entirety of the island of Lesbos. Because of its strategic location as a key position for the Aegean sea routes that connected Italy and the Black Sea, the importance of the Castle was significant, something the Venetians were well aware of from early on and which is eloquently reflected in their constant attempts during the 15th c. to seize Lesbos from the hands of the Ottomans and ultimately dominate the island. From the written tradition of late antiquity, we are informed that the settlement of Agioi Theodoroi was deserted before the 17th c. From there on, the Castle would gradually be completely destroyed.

Today, on the initiative of the Ephorate of Antiquities of Lesbos, under the direction and supervision of the head of the Service, Dr Pavlos Triantafyllidis, excavation work is carried out in order to showcase the important archaeological site of the medieval Castle and of the ancient city of Antissa. Research is focused on the sea wall that runs along the medieval moat, the cross-wall of the five towers and the Upper Castle. Apart from the abundant portable finds (pottery, metal and glass objects, coins) and the underground storage areas in the Upper Castle, the most important finds so far include an arched building of the 7th c. BC and two earlier rectangular buildings of the 10th – 9th c. BC, which represent the transitional period from the Late Bronze Age (1600-1100 BC) to the so-called Dark Ages (11th – 9th c. BC) during which, the movement of the Aeolic tribes to Lesbos, among others, took place in the wider context of the Iron Age Greek Migrations.