It is a marble mask called Mouth of Truth (Bocca della Verità). According to popular belief it was said that any one putting his hand in this mouth and swearing falsely, could not withdraw it. The mask is situated in the atrium of St. Mary's in Cosmedin church.

P.zza della Bocca della Verità

(Via dei Cerchi) 15, 90, 90/, 160

Admission free