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:Sigmaringen Castle was first mentioned in the year 1077 in the chronicles of Petershausen monastery. The oldest parts of the castle are concealed beneath the alterations made during the 17th and the 19th centuries. The secret of the earliest settlement built on this defendable rock will never be fully revealed: large-scale excavation work would be necessary, which the extensive land development renders impossible. Judging from the many Roman remains unearthed in the area around Sigmaringen, the 12th century keep known as the 'Roman Tower' could be traced back to a Roman predecessor.
The castle remains that have been preserved (gate, great hall and keep) date back to the Staufer period around 1200. The castle remains were integrated into subsequent buildings. The foundations of the castle buildings are to a large extent identical to the surrounding castle wall.
These remains give us a good idea of how the castle might have looked during the 12th century.