Castra ad Montanesium is a ruined Roman fortress in the town of Montana, Bulgaria. It was built as the town grew to greater importance as a Roman settlement. Near the entrance of fortress are the ruins of the basilica. The built tourist path passes along it and leads to the fortress walls, behind which there is another church, though it is smaller.
The fortress was constructed in the first century AD to give a defensive buff to the Roman town of Montanesium. During the reign of Constantine the Great (306-337) an early Christian basilica was constructed adjacent to the complex.
Between 440 and 490, the northwest of modern Bulgaria was devastated by the raids of the Huns, under Attila, and the Goths. Later raids by the Slavs and Avars between 500 and 560 resulted in the destruction of the fortress down to its foundations, along with most of Montanesium.
In the early 2010s, an initiative was undertaken to restore parts of the basilica and fortress, as a part of the second stage of the EU's Regional development program.
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.