Considering the Residenz am Zuckerberg in Trier?
A VT member wrote the following comment about visiting Trier:
Go to the Porta Nigra A Roman... by houba
Go to the Porta Nigra A Roman port from the second century. It is the only big part of the wall surrounding the ancient city wich has survived.
Another part is the Arena /amphitheatre, which was admitted in the later build wall, and wich was also used as a port to the city