The fort of Contra Aquincum, excavated on the Pest side, next to the modern-day Erzsébet bridge, was constructed to protect the river crossing.
The rhomboidal fort (86 m x 84 m) fortified with horseshoe-shaped towers, was probably built in 294, but there had already been a large fort on its site from the 2nd century. The conserved ruins of a section of its northern wall and two towers can be viewed on site.
Based on recent research, the fort on Március 15 Square, previously known as Contra Aquincum, was likely called castellum contra Teutanum or castellum contra montem Teutani (fort opposite the mount of Teutanus). Hence Contra Aquincum may properly be applied to the fort at the mouth of the Rákos stream, previously known as Transaquincum.