Didymoteichon is first mentioned as a bishopric in the 9th century. According to some scholars, it was the city succeeding ancient Plotinopolis, which was defended by emperor Justinian. It was recently discovered, however, that Didymoteichon was also protected with a fortification wall dated to the period of Justinian. It seems then that the name "Didymoteichon" ("twin walls" in Greek) was used for the two opposite fortified cities, "the twin castles". The twin hills control the road that linked Traianoupolis and Adrianople. The fortification is preserved in good condition, without serious problems.
Didymoteichon was the birthplace of the emperor of the state of Nicaea, John III Vatatzes (1222-1254) and of John V Palaiologos (1341-1347). It was here that John VI Kantakouzenos was crowned emperor in 1341, and in 1713 the king of Sweden Carl XII was imprisoned by the Turks.
The site was first investigated in 1970 but systematic excavations started in 1985. Eight basements of Byzantine houses have been revealed, along with one gateway, one tower, part of the wall and a section of the rampart. Also excavated is the small church of St Catherine, of the Palaiologan period, and a cemetery chapel (?) of the same date, outside the church of St Athanasios.