The Mouth of Truth is an ancient Roman marble mask in Rome, Italy, which stands against the left wall of the portico of the Santa Maria in Cosmedin church, at the Piazza della Bocca della Verità, the site of the ancient Forum Boarium (the ancient cattle market). According to enduring medieval legend, it will bite off the hand of any liar who places their hand in its mouth,or,alternatively, any who utters a lie while their hand is in the mouth.It still attracts many visitors who insert their hands.

The massive marble mask weighs about 1300 kg (2800 lbs) and probably depicts the face of the sea titan god Oceanus. The eyes, nostrils and mouth are open. Historians aren’t quite certain what the original purpose of the disc was.