Iron Tower

Not long after 350, in the course of the abandonment of the Roman camp, this wall was lowered and rubble (spolia) from earlier construction used to enlarge and strengthen it.

After the Romans withdrew, it was improved at various times, particularly in the Merovingian and Carolingian periods, becoming what archaeologists studying the city have called the "Roman-Carolingian" wall.

[1] However, Mainz was an important political and strategic ally in the Hohenstaufens' struggle for supremacy in the German Empire against the Welfs, and so in circa 1190–1200 the city was granted permission to rebuild the defences.

[1] On the Rhine side, the arch is embellished with two Romanesque carvings of lions in sandstone, atop ornamental capitals over fluted cornerstones.

Towards the end of the 16th century (or possibly as early as the start of the 14th), the gateway lost its function and the entrance to the city was moved to the so-called "Little Iron Door" (Eisentürlein) in a smaller building attached to the tower.

Beginning in the 17th century, the upper stories of the Iron Tower were used as the main goal of what was then the French city of Mayence.

Prominent prisoners held there included some officers of the Lützow Free Corps in 1813, and the Mainz revolutionaries from the March Revolution of 1848/49 until they were pardoned in 1850.

On both sides of the tower, the adjacent buildings and a portion of the city wall were reconstructed to reproduce the medieval structures as accurately as possible.