Arch of Janus

Listen for a moment. Traffic hums along the road behind you, but here, at the foot of this square block of marble, the sound seems to soften. The stone in front of you is grey and pale gold, pitted with small holes, and rough in places like old bread crust. You are standing in a low dip between two of Rome's hills. Long ago, this ground was wet, marshy and often flooded by the Tiber. Today it holds one of the strangest arches in the city.

This is the Arch of Janus. Most Roman arches you may know, like the Arch of Constantine near the Colosseum, are flat monuments with one face for a procession to pass through. This one is different. It has four faces and four openings, one on each side. Architects call this a quadrifrons — a Latin word that simply means four-fronted. It does not mark a single road. It stands over a crossing, a covered meeting point where paths came together.

Here is the first surprise. The name has almost nothing to do with the god Janus. Janus was the Roman god of doorways and beginnings, the one with two faces looking in opposite directions. But in Latin, the word ianus could also mean a covered passage or an archway. Over the centuries, people connected this four-way passage with the god of doors. The name stuck. The ancient Romans themselves, however, probably called it something else entirely.

Most scholars date the arch to the early fourth century, the age of the emperor Constantine and his sons. A list of Roman monuments from that century mentions an arch of the deified Constantine in this district. Many historians believe this is that arch. It may have honoured Constantine himself or been raised by one of his successors. The exact dedication is not certain, and no inscription survives to settle the question.

Now look closely at the walls of the piers. You will see rows of shallow niches, each one topped by a carved half-shell, like a scallop. There are many of them, stacked in two levels on every face. It is natural to imagine a statue standing in each one. Yet some scholars suspect that many niches were decorative and may never have held figures at all. The effect is still powerful — a rhythm of light and shadow across the marble.

The next detail is easy to miss. Look up at the keystones, the central stones at the top of each arch. On some of them you can still find worn carved figures. Time and weather have rubbed away most of their features. They are usually identified as goddesses, figures who once watched over the people passing beneath. Today they look more like soft shapes in the stone, but they are original decoration from late antiquity.

Those small holes all over the surface tell another story. Roman builders often held blocks of stone together with metal clamps. In the Middle Ages, metal was valuable, and people chiselled into old monuments to pull the clamps out and reuse them. Across Rome you will find ancient buildings scarred in exactly this way. Here, the holes make the arch look almost moth-eaten. Each one marks a moment when someone saw this monument as a source of raw material.

In the Middle Ages, the arch had a very different role. A powerful Roman family, the Frangipane, turned it into part of a fortress. They built a tower on top and used the solid structure as a stronghold. Rome at that time was a city of rival noble families, and many ancient ruins became castles. A four-sided arch with thick piers was an ideal base. For centuries, it guarded a family's power instead of a crossroads.

Here is the second surprise. The arch you see today is shorter than the original. In the nineteenth century, restorers removed the medieval additions from the top. Along with them, they took down the attic, the upper block of the arch. They believed it was a medieval addition too. In fact, it was part of the ancient design. So the flat top you see now is the result of a well-meaning mistake, and the arch has lost part of its original height.

Turn slightly and look at the church beside you. This is San Giorgio in Velabro, a small and very old church dedicated to Saint George. Attached to its side is another, much smaller ancient monument, often called the Arch of the Moneychangers. It was raised by local merchants and bankers in honour of the emperor Septimius Severus and his family, around two centuries before the Arch of Janus. Two ancient arches, side by side, from two different ages of the empire.

The name of this area, the Velabrum, recalls the marshy land that once lay here. Nearby was the Forum Boarium, the old cattle market of Rome, close to the river port. Traders, herders and dock workers once crowded these streets. Locals tell the old legend that Romulus and Remus, the founders of Rome, were washed ashore somewhere in this low ground. That is a story, not history, but it shows how deeply this place sits in the city's memory.

The neighbourhood carries more recent memories too. In 1993, a car bomb exploded in front of San Giorgio in Velabro and badly damaged the church porch. It was one of several attacks in Italy that year linked to the Mafia. The church was carefully repaired. When you look at its calm front today, it is hard to imagine that violence. It is a reminder that even very old places are part of the present.

The arch is fenced off, so you cannot walk through its openings as Romans once did. But you can walk around it and see each face. Notice how the light changes from side to side. One face may be bright and warm, while another rests in shade. The niches catch these changes most clearly, like a row of small dark windows.

Before you leave, stand still for one more moment. Picture a covered crossing with people stepping out of the rain, merchants talking, carts rolling past. Then look again at the pitted marble in front of you, at the missing clamps, the flat top, the faded goddesses. Everything here has been used, changed and reused. As you walk on towards the river, listen to the traffic again... and remember that this low ground has always been a place where roads meet.