Alba Iulia has always played an important role in the history of Transylvania. Its first fortification was the castrum of the Roman Legio XIII Gemina, the ruins of which were used in building a medieval castle serving as the administrative and religious centre of Transylvania. This castle was further fortified in the 18th century, based on the drafts of G. M. VISCONTI. The most representative elements of the present Vauban Fortress are the richly ornamented baroque monumental portals.

The now ruined castle, located in the town centre, was the seat of the BÁTHORY family's Somlyó branch. A mansion, already standing there in 1508, was rebuilt during the 16-17th centuries into a castle with a rectangular ground-plan, strengthened by three circular towers and a rectangular one. This inner castle was protected by a fortification with Italian bastions. Up to the present, only two circular towers, two bastions, the fortification's gate building and some wall fragments have survived, their conservation and rehabilitation are in process.