I'm taking a class called Art of Rome, which is an on-site class that takes us to historical monuments such as The Colosseum and temples that were built for the Gods.
For our first trip, we visited the church of St. Mary, which is right across the street from The Round Temple. Both are in the center of Rome. The Bocca della Verita is mounted on the wall at the left end of the entrance porch. It is a large marble disc, originally a fountainhead, with the head of a river god. In the time of the Gods it was believed that the Bocca della Verita (the mouth of truth) would bite off the hand of those who tell lies.