Beware the Mouth of Truth!

Given the exalted position the Bocca della Verità holds in the Roman cultural imagination, it may come as something of a surprise that its origins are rather humble.

The exact original function of the massive marble disc is still open to question, but given its shape, size and the wear patterns in the stone, the most plausible hypothesis holds that this huge decorated face was originally a ceremonial drain cover — most likely for the nearby Cloaca Maxima, ancient Rome’s vast main sewer, whose still-extant channel flows into the Tiber just a short distance from Santa Maria in Cosmedin.

Elaborately carved marble drain covers taking the form of faces were not unknown in antiquity. In the 16th century a mask very similar to the Bocca was set into the floor of the Palazzo della Cancelleria, sparking a brief fashion among Rome’s grander households for displaying recovered ancient drain covers as objects of prestige.

The face likely represents the sea-god Oceanus, identifiable by what appear to be the god’s distinctive crab-claw “horns” above his ears. As the mythological source of all water on earth, Oceanus was a fitting guardian for the city’s water infrastructure.

This is just one hypothesis, however. Other scholars argue that the symbolic weight of the face suggests it originally belonged to a cult building rather than a sewer — perhaps the nearby circular Temple of Hercules Victor, just visible from the church entrance, or the ancient Ara Maxima, the altar of Hercules that once occupied the very site on which Santa Maria in Cosmedin later stood.

In antiquity this was a place where oaths were taken, contracts sealed and vows made before the gods — a function that resonates with the mask’s later legendary role as a detector of liars. We simply cannot say which hypothesis is correct.

What we can say is that the disc is an extremely fine piece of Roman sculpture, carved in pavonazzetto (Phrygian marble), measuring about 1.75 metres in diameter and weighing approximately 1,300 kilograms — significantly heavier than it looks.

Despite the many learned and plausible hypotheses about its ancient origins, we know absolutely nothing certain about the Bocca’s history before 1450, when it first appears in the historical record leaning against the side of the church.

In Antonio Tempesta’s meticulous 1590s map of Rome, the huge face is clearly visible propped against the facade — a familiar landmark rather than a new arrival.

It seems likely that the mask had lain somewhere in the immediate vicinity for centuries before this; 12th-century decorations within the church depict masks strikingly similar to the Bocca, suggesting it was a known feature of the site long before the written record picks it up.

At some point in the early 17th century the marble was mounted against the church facade, and in 1631 it was finally given its current position set into the covered narthex (entrance porch) of Santa Maria in Cosmedin, where it has glowered at visitors ever since.

Whatever its murky ancient history, by the 15th century the mask had taken on a new symbolic life in the cultural imagination of the city.

Perhaps lending credence to the theory that the Bocca originated at a site where oaths were made, 15th-century sources record that the weighty marble face was believed to have the magical power to detect liars — particularly adulterous wives — by biting off the perjuror’s hand thrust into its mouth, in a bizarre echo of medieval trial-by-ordeal.

Whether the usually cynical Romans genuinely believed this is debatable; as lovers of a good story, many probably relished the legend without taking it literally.

By the late 18th century the Bocca was arbitrating on all manner of disputes beyond marital fidelity, and its role as a lapidary lie-detector had been firmly established in popular imagination. Even Sigmund Freud, not generally a man given to superstition, felt compelled to try it.

Right up there alongside Anita Ekberg’s nocturnal plunge into the Trevi Fountain in Fellini’s La Dolce Vita, it is one of the most iconic moments in the cinema of Rome: midway through William Wyler’s Roman Holiday (1953), Gregory Peck’s hard-boiled American reporter Joe takes princess-on-the-run Audrey Hepburn on a whistle-stop tour of the Eternal City on his Vespa.

Stopping off at Santa Maria in Cosmedin, Joe recounts the legend of the Mouth, whereupon a nervous Hepburn gingerly inserts her hand. Nothing happens.

When it is Peck’s turn, he inserts his hand and immediately begins roaring in apparent agony, pulling out what appears to be a stump — before quickly revealing that his hand was simply tucked into his sleeve.

According to a pleasing piece of cinematic legend, the ruse was entirely improvised and genuinely frightened Hepburn — hence her entirely authentic look of shock and relief.

The scene was not in the original script. Peck improvised it on the day, and Wyler kept it in because Hepburn’s reaction was too real to discard.

The vast majority of visitors that line up in the narthex of Santa Maria in Cosmedin to have their photo taken with their hand thrust into Oceanus’ mouth barely give the church itself a second thought, and certainly don’t bother stepping inside. Don’t make their mistake! Santa Maria in Cosmedin is one of the finest examples of medieval ecclesiastical architecture in Rome, and a church that deserves to be far better known.

The brick campanile, rising in elegant tiers studded with decorative discs of purple and green marble, is one of the most beautiful medieval bell towers in the entire city.

The interior is remarkable: repurposed and mismatched ancient Roman columns divide the nave and side aisles in the manner typical of early Christian churches. An altar in the left hand aisle of the church conserves the reputed skull of Saint Valentine, one of the city’s most interesting relics.

The floor is a masterpiece of Cosmatesque craftsmanship — that characteristically Roman medieval style of geometric patterning in polychrome marble — and the raised schola cantorum at the centre of the nave, a liturgical enclosure reserved for the choir, is one of the very few surviving examples of this once-universal feature of medieval church architecture.

Don’t miss the Gothic baldacchino over the altar, the medieval frescoes, or the extraordinary 8th-century crypt below, carved directly into the surviving remains of the ancient Ara Maxima — the altar of Hercules — beneath the church floor.

And while you are in the narthex, don’t rush past the impressive monument to Cardinal Alphanus on the left-hand wall, one of the finest medieval tomb sculptures in Rome.

The extremely tall brick campanile is one of the most beautiful in all of Rome, studded with decorative disks of purple and green marble. Don’t miss the impressive monument to the 12th century papal chamberlain Cardinal Alphanus in the narthex.