The Mouth of Truth

Empire · It’s Really a Drain Cover

This famous disc was most likely an ancient Roman drain cover carved as a river-god.

The "Mouth of Truth" is an ancient Roman marble disc nearly two metres across, carved with a bearded male face (usually taken for a sea- or Tiber-god). Scholars generally hold it was originally a cover or ornament for some part of Rome’s drainage — the city’s advanced sewers (like the Cloaca Maxima) needed such covers. A two-thousand-year-old piece of municipal infrastructure was later set into a church wall and became something tourists line up for worldwide.

Sources：Santa Maria in Cosmedin　·　Studies of the ancient Roman drainage system

↑ Because of the last layer：Precisely because it was a mysterious, solemn ancient Roman god-face, the Middle Ages attached to it the power to "tell true from false and bite the lie."

Today · The Hand a Liar Loses

A medieval legend says the mouth bites off a liar’s hand; Roman Holiday made it world-famous.

From the Middle Ages a legend spread: put your hand in the "Mouth of Truth," and if you have lied, it will bite your hand off. This lie-detector myth made it a prop for oaths and tests of loyalty. In the 1953 film Roman Holiday, the scene where Gregory Peck pretends the mouth has seized his hand, terrifying Audrey Hepburn, made it overnight one of Rome’s most famous sights. A drain cover, through a legend and a film, came to live as the embodiment of "truth."

Sources：Roman Holiday (film, 1953)