Castra ad Montanesium is a ruined Roman fortress in Montana, Bulgaria. It was Info center Info center settlement.

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.