Due to its geographic position between Constantinople and Thessaloniki, Thrace played an important role in the long history of the Byzantine Empire from early Christian years to the fall of Constantinople (1453). Being a natural fortification to the north of the state it was organised both administratively and militarily. It faced, for centuries, the attacks and the destructions caused by various hostile tribes and nations, the heaviest of all by Ioannitsi, king of the Bulgarians, in 1206. Topeiros, Xanthi, Avdira, Anastasioupolis, Mosynopolis, Komotini, Gratini, Maronia, Makri, Traianoupolis, Pheres, Didymoteichon and Pytheion are Byzantine towns, in ruins nowadays , that the visitor sees when passing through Thrace. Most of the aforementioned towns were used as stations by the travellers of the Egnatia road – the most important road across Thrace – and developed economically, socially and militarily. Many served as seats of bishops and other functionaries of the church, some were built close to or on the site of ancient towns, others keep until today their Byzantine name. The Papikion Mountain, part of the mountain range of Rhodopi, is important to the religious life of Byzantium, since an important monastic centre developed there along the lines of Mount Athos. The aforementioned towns along with smaller settlements and fortresses standing on the barely accessible mountaintops of Rhodopi safeguarded and controlled communication in the entire Thracian region and transmitted the Byzantine civilization to to the insular Balkans.