Hehe...
Well, the can always use some pillars to hold the building of course. In a nearby shopping mall they preserved (and incorporated in the building) a whole big, public Roman bath.
On another project I also worked, the Roman early Christian church was partly under a late Baroque, late 18th - early 19th century, three storey plebendary and chapters building so when we excavated it (and the protection building and visitors' centre was being built), they had to dig down to about 8-10 metres section by section to "undermine" the foundetions and fill it up with concrete.
Well, surely it was a big project; about 13 K cubic metres and € 6 million spent over almost three years.