Like everything in Europe the old things we visit now as tourist attractions are built on top of even older ruins and when they find these we pay more to see them too.
This was the site of the baptismal font just in front of the duomo which is now under the stairs and piazza.
They found quite a few artefacts from that time including coins. They probably weren’t tossed into the baptism font, but who knows maybe people liked throwing money into pools of water in ancient times too.
