“After an hour in the Forum, someone asked me when we were going to see the important part. We had already walked past it. He had photographed the brick building without knowing what it was.”

The question sounds like impatience. It is not. It is a reasonable response to a place that gives the visitor very little to recognise.

The Roman Forum is one of the most famous archaeological sites in the world, yet on the ground it can be surprisingly difficult to read.

Why it looks like nothing

Because the Forum was never one building.

It was the working centre of a city: temples, law courts, archives, meeting halls, basilicas, speaking platforms and shops, built and rebuilt beside one another over many centuries.

After antiquity, much of that architecture was abandoned or transformed. Marble was reused, stone was carried into later buildings, ancient structures disappeared beneath accumulated earth, and the level of the city gradually changed.

By the early modern period, part of the area was known as the Campo Vaccino — the cattle field.

What visitors walk through today is therefore not an intact ancient city preserved in place. It is an archaeological landscape revealed through centuries of excavation.

That is why it can look almost like an architectural plan drawn directly onto the ground.

Except for one building

At the northern end of the Forum stands something completely different: a tall rectangular brick hall with a roof, an enormous plain façade and almost none of the visual drama visitors expect from ancient Rome.

Many people assume it is later.

It is the Curia Iulia — the Senate House.

Julius Caesar began the new Senate House as part of his transformation of the Forum. The building was completed under Augustus.

The structure visible today largely reflects the rebuilding carried out under Diocletian after a fire in the late third century AD.

Its survival has a great deal to do with what happened afterwards.

In the seventh century the Curia was converted into the church of Sant’Adriano. Ancient buildings that acquired new functions had a better chance of remaining standing because they continued to be used, repaired and inhabited.

In the twentieth century later additions were removed and the building was returned to an appearance intended to reveal its ancient form.

Go inside

The exterior explains why people overlook it. The interior explains why they should not.

The room is severe, high and almost startlingly intact compared with the landscape outside.

Along the sides are the low stepped areas associated with the seating of the senators. Between them stretches the central floor of the chamber.

Most striking is the surviving late-antique marble pavement: coloured stone laid out in geometric patterns across the floor.

What to look at

First, forget the objects and look at the proportions.

Stand in the centre and look from one side of the chamber to the other. The room suddenly stops being an archaeological ruin and starts behaving like architecture again.

Then look down.

The marble pavement is not decoration added to make the building easier to understand. It belongs to the ancient history of the room itself.

Finally, turn towards the entrance.

The doors are no longer here

One of the strangest chapters in the history of the Curia is attached to its monumental bronze doors.

The ancient doors were removed in the seventeenth century during the pontificate of Alexander VII and transferred to the Basilica of St John Lateran.

Francesco Borromini adapted them to their new setting, adding bronze elements around the ancient doors so that they would fit the much larger Lateran portal.

They remain there today.

The doors of the Roman Senate are still in Rome. They are simply three kilometres away, opening into a church.

What this changes

The Forum does not really have a single centrepiece. Looking for one is part of what makes the site difficult to understand.

Its meaning comes from relationships: one building beside another, one political institution beside a temple, one street crossing another, one century built directly over the remains of the previous one.

The Curia is valuable because for a moment all of that abstraction disappears.

You are no longer looking at foundations and trying to imagine walls.

You walk into a room.

The important part is not further ahead. It is the plain brick building you may already have photographed without knowing what it was.

In the Roman Forum, survival can make an ancient building look less ancient than the ruins around it.