The fortification on the hill of Kales
Above the town of Didymoteicho, at the top of Kales hill is the castle. Its walls have a total length of 1 km and their height is preserved at about 12 m. Perimetrically it is reinforced by circular and square towers that were originally 24. Its strategic point, the fortified nature of the castle, as well as the way it was built, in some places, do not exclude the possibility that a castle pre-existed earlier than the Byzantine period. It is certain, though, that the walls took their final form in the 6th century AD and in the following centuries they were strengthened and maintained. During the turbulent times of the Byzantine civil wars, at the beginning of the 14th century, the castle was the base of the claimants to the Byzantine throne and a battlefield. After the occupation of Didymoteicho by the Ottomans, in 1361, the castle began to decline as it was no longer a priority for the protection of the area. It suffered severe damage from raids during the post-Byzantine period but also during the Russian-Turkish wars, 1828 and 1878.
The castle is connected by an underground passage with the cave of Vouva.