Yes Johannes, I am pretty sure I got it:

For about one century the Magna Aula (as the Romans called it) was used as the Emperor's throne hall. During the Merowingian aera it became the residence of the royal magnates - the Franks destroyed the roof and the Roman furnishing (mosaiques, statues, underfloor heating...)and built a settlement inside the ruin.

From 1198 onwards the Archbishop of Trier used it as administrative centre and residence.

After even having been (mis-)used as military barracks, it was changed into a Protestant church under King Friedrich Wilhelm IV. of Prussia, as which it is used still today.


I hope this was specific enough....