"ancient Roman ruins" You might find that the Roman presence was built upon an even earlier site. That happens very often - the Romans were very good at colonizing, whilst fitting in. They would often embrace the local religions and simply add them to their pantheon.

I've just read this: https://en.wikipedia.org/wiki/Church_of_St._Donatus and there are no notes about pre-Roman ie iron age archaeology.

The church looks stunning and the acoustics will probably be amazing.