After the fall of the Upper German Limes in AD 259. Began under Emperor Diocletian (285 - 337), the work continued, and under Valentinian I (364 - 375) it was strengthened. This last stage included the construction of the Rhine bridge at TENEDO / Zurzach, which was protected on the left bank of the Rhine by the massive double fort (Kirchlibuck and Sidelen) and on the opposite side by a bridgehead (Reinheim). On the street that led to the bridge in the bar between the two fort plateaus was a bathing building.
After the withdrawal of the Roman troops (401), the thick fort walls offered protection for the local civilian population. Even before the year 1000, a new settlement gradually arose west of the fort, near the grave church of St. Verena in the Roman cemetery, the core of what is now Zurzach. The fort buildings gradually fell into disrepair, and only some of the walls of the larger of the two forts (Kirchlibuck) were able to withstand the ravages of time; the surrounding walls on the slope side are likely to have fallen into the Rheinnn in the course of time.