City in Germany on the Rhine noted as the seat of imperial diets (5)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
worms
(Other definitions for worms that I've seen before include "Long soft-bodied limbless invertebrates" , "Burrowing invertebrates" , "Where reformer was condemned" , "despicable people" , "harmful programs" .)