It is a marble mask which stands against the left wall of the portico of Santa Maria in Cosmedin church. As a lie-detector from another time, it attracts thousands of visitors who audaciously stick their hand in the mouth. According to legend, a liar who puts his hand in the mouth will have it bitten off. Fotograph fee required: € 5. In the proximity you can admire the round temple of Hercules Victor and the Temple of Portunus, one of the best preserved of all Roman monuments.