Mosynopolis , of which only ruins now remain in Greek Thrace, was a city in the Roman province of Rhodope, which was known until the 9th century as Maximianopolis. The city of Maximianopolis appears in written sources from the 4th century on. Its fortifications were renewed by Byzantine emperor Justinian I, and it was later a base for operations by Emperor Basil II in his wars against the Bulgarians.
In the 11th century, the city was the center of a district (bandon) in the theme of Boleron, and Anna Komnene reports in her Alexiad that there were many Manichaeans living in Mosynopolis in the late 11th/early 12th centuries. The town was captured in 1185 by the Normans, while the monk Ephrem says that the city was captured in 1190 by Frederick I, Holy Roman Emperor. The Battle of Messinopolis, in which the Bulgarians defeated Boniface I, Marquess of Montferrat, took place nearby in 1207, and was speedily followed by the destruction of Mosynopolis by Tsar Kaloyan of Bulgaria.
Bishops of Maximianopolis in Rhodope were present at the 5th and 6th-century ecumenical councils of Ephesus (431), Chalcedon (451), and Constantinople II (553) and in another council of 459. From the 7th to the 9th centuries, the see is referred to as archiepiscopal, giving it autocephalous status.
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.