Castra ad Montanesium is a ruined Roman fortress in the town of Montana, Bulgaria.

The built tourist path passes along it and leads to the fortress walls, behind which there is another church, though it is smaller.

[1] 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.

[2] The fortress is a central part of Montana's history, culture and tourism, being one of the oldest and most impressive structures in the town.