On the outskirts of Alexandroupoli, close to the village of Avantas, lie the medieval castles of Avantas and Potamos. Three different historic eras coexist on those walls, namely the Mycenaean, Classical and the Byzantine era. Both these castles supervised the field and controlled the passages towards the plains of Komotini and inland of the Rodopi mountain range.
Both constructions date to the second half of the 13th century or the first half of the 14th and they are both erected next to streams and on top of steep hills. The Avantas castle is shaped with a simple transverse wall that severs any access to the slope and the peak of the hill. In Potamos the castle has 3 towers that form an internal enclosure and a further external one.
Avantas castle consists of a wall of approximately 140 meters, parallel to the contours and a second, about 40 meters, almost perpendicular to it. The fortified area is of a generally oblique rectangular shape and is slightly less than 1 hectare. The fortification is developed on the slope from which it is possible to rise on the hill, while the rest is not protected by walls because the rough terrain is enough.The fortification was reinforced by four rectangular towers. There were two gates: one at the end of the wall protected by a tower and one in the middle of the wall, between two towers. There are no architectural remains, which might testify residential occupation. The oldest construction elements are some massive domes that have been used in various parts of the fortification which might indicate an older fortification.
References:The Church of St Donatus name refers to Donatus of Zadar, who began construction on this church in the 9th century and ended it on the northeastern part of the Roman forum. It is the largest Pre-Romanesque building in Croatia.
The beginning of the building of the church was placed to the second half of the 8th century, and it is supposed to have been completed in the 9th century. The Zadar bishop and diplomat Donat (8th and 9th centuries) is credited with the building of the church. He led the representations of the Dalmatian cities to Constantinople and Charles the Great, which is why this church bears slight resemblance to Charlemagne's court chapels, especially the one in Aachen, and also to the Basilica of San Vitale in Ravenna. It belongs to the Pre-Romanesque architectural period.
The circular church, formerly domed, is 27 m high and is characterised by simplicity and technical primitivism.