For our visit to San Nicola in Carcere we head towards the Tiber River from the Piazza Venezia, just past the Theater of Marcellus. When you look at the structure, you can see that parts of ancient buildings appear to be embedded within it. The church is, in fact, built by re-using the remains of ancient Roman temples. These temples date back to the 2nd and 3rd centuries BC, in the time of the Roman Republic, well before the Roman Empire.