Historic water mark in a staircase in the Bonner Münster marking the 1784 flood level.
Cities in the Rhine region in west Germany have been subject to floodings for centuries. In 1784 a particularly severe flooding event occured during a particularly cold winter. Here is a text from a website on the history of Cologne. (my translations)
The centennial ice drift
After the extreme winter of 1783/84, one of the largest floods in historical times hit Central Europe. Evidence of severe destruction has been passed down from Regensburg, Bamberg, Heidelberg, but especially from Cologne.
At the beginning of January 1784, the frozen Rhine reached an ice thickness of 3 meters. The drifting ice floes from the Upper Rhine continued to build up and form large icebergs. Experienced boatmen warned of the dangers of the thaw. In the early morning of February 27th, cannon shots announced that the ice was beginning to move. Starting at the Bayenturm, the ice floes swept everything away. Ships attached to the quay wall and cranes at the harbor were swept away. The subsequent masses of water caused devastating damage. Compared to today’s water level, the flood waters reached a height of over 13 meters. On the Cologne side, 27 deaths are reported; in the then independent city of Mülheim, 30 human casualties were recorded.