In the mid-4th century, the city wall that had existed until then, originally dating back to the 3rd century, was renovated. The wall was significantly shortened, so that the Roman theater, the abandoned legionary camp, and other central parts of the city were located outside. In the renovation, old building stones (spolia) from the barracks were reused. The sandstone paving of the camp road, which led to the former porta praetoria, remained in use. To allow the use of this important road, the city wall was interrupted at this point by a gate. The diagonal red sandstone slabs of the road have been preserved to this day.
The Roman Gate is located in Mainz-Oberstadt on Kästrich at house number 61. During excavations in 1985, the city gate, remnants of the camp road, and adjacent wall sections were uncovered. The sandstone slabs of the via praetoria clearly show tire tracks nearly two meters wide, corresponding to the wheel widths of Roman carts, evidencing frequent use of the road.
The city gate was discovered during the construction of a residential complex on Kästrich and is now integrated into it, allowing visitors to freely enter. The remains of the double-walled structure and the gate lie about three meters below the current street level; two stairs provide access.
The structure is preserved at base height and is considered the only Roman city gate found in Mainz. Moreover, it is one of the most recent Roman city gates in Germany.
Nearby is the medieval Altertum, which was probably built on Roman foundations and marks the location of one of the numerous towers of the Roman city wall.
