The Mouth of Truth is located on the portico of the Santa Maria in Cosmedin Church in Rome. It measures 1.75 metres in diameter and is the face of a man made from marble. In the Middle Ages there was a famous legend which claimed that the stone had powers. It was believed that the Mouth of Truth was a lie detector, and so if someone lied while their hand was in its mouth, the stone would bite off their hand.
Rome Guide | Monuments in Rome