Bocca della Verità in Bardiglio marble our reproduction

La Bocca della Verità (English: the Mouth of Truth) is an image, carved from Pavonazzo marble, of a man-like face, located in the portico of the church of Santa Maria in Cosmedin in Rome, Italy. The sculpture is thought to be part of a first-century ancient Roman fountain, or perhaps a manhole cover, portraying one of several possible pagan gods, probably Oceanus. Most Romans believe that the 'Bocca' represents the ancient god of the river Tiber.

The most famous characteristic of the Mouth, however, is its role as a lie detector. Starting from the Middle Ages, it was believed that if one told a lie with one's hand in the mouth of the sculpture, it would be bitten off. There was also a medieval legend, wrongly believed to originate with the Roman poet Virgil, of an adulterous empress who managed to deceive her husband in a trial using the Mouth. This is an infrequent subject in medieval and Renaissance art, forming part of the Power of Women literary topos. The piece was placed in the portico of the Santa Maria in Cosmedin in the 17th century. This church is also home to the relics of Saint Valentine.