As dendrochronological studies of wooden pile grids of the wall sections running parallel to the Rhine show, Mogontiacum was surrounded by its own city fortifications with walls and rectangular, slightly protruding towers as early as the middle of the 3rd century.[1] After the fall of the Limes, repairs were carried out on the Roman city wall, especially in the Merovingian period under Theudebert I and Sidonius, as well as in the Carolingian period. In Mainz city archaeology, this city wall is therefore referred to as "Roman-Carolingian".
After Mainz ministerials and citizens killed their archbishop Arnold von Selenhofen in a conflict over tax collection, the Hohenstaufen Emperor Frederick I Barbarossa imposed the imperial ban on the city in 1163 as punishment. Its city wall and its towers were to be demolished. According to some historians, this was limited to the destruction of the gate towers.
In the dispute between the Staufers and the Guelphs for supremacy in Germany, the city of Mainz was an important political and strategic ally, so permission to rebuild the city fortifications was granted as early as 1190/1200. The Roman-German King Philip of Swabia was able to see for himself the desolate state of the fortifications at his coronation in Mainz Cathedral in 1198. It is historically proven that construction on the city wall began in 1200 at the latest. In the copy book of St. Peter's Abbey there is a document dated 4 July 1200 in which the city demands five marks of silver from the canons for the reconstruction. The high lords had helped themselves to the demolition stones and built their houses with them.[2] During this construction phase, the Fish Gate was also built as one of a total of 34 gate and watchtowers.