The vertical rocks of the acropolis-fortress of the byzantine town of Tarsos, the historic castle of rocks, is located in the small village of Tarsos, on the borders of the municipality of Sikyon, in the mountains of Aroania and Cyllene, or Chelmos and Ziria. The church of the Dormition of Our Lady, Our Lady of the Rocks, is built in a mountain slip. It has been listed as a byzantine landmark since 1962. Tradition attests that the church was founded when Muhammad II had arrived in the region (1458), and besieged and conquered the castle of Tarsos. There is no historic evidence that documents or denies the legend. It is possible that the foundation of the church dates back to the period of Muhammad the Conqueror. Access to the church during winter is very difficult, especially when it snows. To reach Tarsos visitors has to pass through the region of Stymphalia or through the village of Trikala.
In antiquity there is no reference to a village or town under the name Tarsos, but the word existed and had many meanings. The byzantine town Tarsos is a consequence of Slav invasions that begun in the late 6th century A.D. and ended in the late 8th century. It is possible that the fortress of Tarsos was a shelter during the Slav invasions. On a golden bull of emperor Nikephoros A (802-811) it is attested that the dioceses of S(t)arsokoroni, Lacedaimonia and Methoni pertain to the metropolis of Palaion Patron. The existence of a diocese presupposes the existence of a small town. The monastery operated as a shelter also during the Ottoman occupation.
The church is hewn in a rock a few meters below the top. The entrance is located about ten meters above the foothill. A stone stairway, attached to the rock, leads to the entrance, where a stone propylon with four columns forms arches. The entrance of the church is located to the west. The icon of Our Lady stands on the north side of the propylon, in a groove in the rock. The propylon offers a magnificent view of the Olvios valley that begins from Karya and extends to the sinkholes of Pheneos. At the background lies Cyllene, the birth place of Hermes.
From the propylion, a low, narrow entrance scarcely lighted by a light hall, leads to the first chamber (3x4meters).
Another small vaulted entrance leads to the second chamber (4 × 6 meters) and then to the main church, a square chamber of 4×4 meters. The church is north oriented, imposed by the location of the rock. In the sanctuary, fresh water flows from the rock. On the rooftop of the main church there is a small opening lighting the main church and the sanctuary. The scarce treasures of the monastery stand around those two chambers.
The feast day of the church is on August 23rd. Although the church honors the Dormitorion of Our Lady, the old portable icon of Our Lady Vrefokratousa (holding infant Jesus) attracts the pilgrims’ attention. The name of artist who painted the icon and the its origin still remain unknown. The face of Our Lady does not belong to the byzantine style.
To the west of the main church, a small opening leads deeper, into the cave. The cave continues to the southwest. In 1998, speleologist made an unsuccessful attempt to explore the cave. Stalactites at 200 meters from the entrance block the way to the cave.