The Mouth of the truth is an ancient marble mask, placed in the wall of the Church of Saint Maria's pronaos of Cosmedin in Rome in 1632. It has a big diameter (1,75 ms) and it represents a faun's face(the nature's divinity), with circular eyes and an open mouth.Its name derives from an ancient tradition: who promised something, inserting the hand into the mouth,would not have been able to extract it if the person was saying the false.The malignant of the epoch, insinuated that the oracle that cut the hand was helped by the judges, that set behind the mask,an executioner armed with a sharp sword.Probably this mask was a fountain or a cloaca's old trap. Another version points it out as coverage of a sacred well of Mercury's temple in the Boario's forum.