Five Paris landmarks and the history visitors walk straight past

Paris is unusually good at hiding things in plain sight. Not in the sense of secret passages — in the sense that a two-thousand-year-old amphitheatre can sit behind an ordinary doorway on a busy street and be walked past by several thousand people a day. What follows is five of those, with the part of the story that is not on the sign.

1. The Roman arena behind a doorway

At 49 rue Monge, in the 5th arrondissement, there is a passage that looks like the entrance to an apartment block. Walk through it and you are standing in a Gallo-Roman amphitheatre from the first century, built when the city was called Lutetia and held something in the order of fifteen thousand people — more than lived in the town itself, which suggests it drew the surrounding region.

The remarkable part is how nearly it did not survive. The arena had been buried and forgotten for centuries, and was rediscovered in 1869 when rue Monge was cut through the hillside. The site was slated to become a tram depot. A preservation campaign formed, Victor Hugo lent his name to it, and the amphitheatre was excavated and eventually opened to the public instead.

Today it is a neighbourhood park. On most afternoons there are people playing football on the floor of a Roman arena, which is either a scandal or the best possible outcome, depending on your view of what monuments are for.

2. The tower with no church

The Tour Saint-Jacques stands alone in a small park near the Châtelet, fifty-two metres of flamboyant Gothic stonework with nothing attached to it. It looks like a folly. It is in fact the bell tower of the church of Saint-Jacques-de-la-Boucherie, built in the early sixteenth century and paid for by the guild of butchers whose quarter this was.

The church was sold off as national property after the Revolution and demolished in 1797 — but the sale came with a condition that the tower be preserved. It then survived by being useful: through the nineteenth century it was leased as a shot tower, where molten lead was dropped from the top into water below, the fall forming it into spheres on the way down. A Gothic bell tower spent decades as a small-arms factory.

There is a statue of Blaise Pascal at its base, commemorating the barometric pressure experiments he carried out there. The tower is now a meteorological station, which is a pleasing continuity.

3. The column attached to nothing

Against the flank of the Bourse de Commerce, in the 1st arrondissement, a fluted Doric column rises about thirty metres and stops. It serves no structural purpose and belongs to no building. Visitors photograph the Bourse and rarely look left.

It was built around 1575 for Catherine de' Medici as part of her Hôtel de la Reine, and it is the only piece of that palace still standing. The hôtel was demolished in 1748; the column was bought and preserved, and later absorbed into the grain hall that eventually became the Bourse. There is a staircase inside it, and a platform at the top.

Tradition holds that Catherine's astrologer Cosimo Ruggieri used it as an observatory. That story is repeated everywhere and is not well evidenced — it may be true, it may be an eighteenth-century embellishment. It is worth knowing both the story and its status, because a good half of what gets told about Paris is of exactly this kind.

4. The medieval city wall beside a school playground

On rue des Jardins-Saint-Paul in the Marais there is a long stretch of rough stone wall with the stumps of two round towers, running alongside a sports ground. There is no barrier and almost no ceremony. It is the largest surviving section of the wall Philippe Auguste built around Paris between roughly 1190 and 1215, before leaving on crusade.

What makes it worth stopping for is what it tells you about scale. This was the edge of the city. Everything beyond it — the Marais as we know it, Bastille, everything east — was fields. Standing at that wall reorganises your mental map of central Paris more effectively than any museum display.

Fragments of the same wall surface elsewhere, often absurdly: in a car park, in the basement of a shop, embedded in the courtyard wall of a private building. Once you know its line, you start finding it.

5. The statue Parisians use as an instrument

On the Pont de l'Alma, a stone soldier — a Zouave, from a French colonial infantry regiment — stands facing upstream with his feet near the waterline. He was one of four military figures on the original 1856 bridge. When the bridge was rebuilt in the early 1970s, only he was kept.

He was kept because Parisians had turned him into a flood gauge. Water at his feet means the Seine is high. Water at his thighs and the riverside expressways close. During the great flood of January 1910, the water reached his shoulders, and that image is still the reference point for how bad it can get.

One caveat that rarely gets mentioned: because the bridge was rebuilt, the Zouave no longer sits at exactly the height he did in 1910, so comparisons between then and now are not strictly like for like. He remains a genuinely useful instrument and an unreliable historical benchmark at the same time.

How to find more of them

The common thread is that none of these are hidden. All five are outdoors, free, and visible from the pavement. What is missing is not access but the sentence that tells you what you are looking at.

• Read the plaques. Paris labels a great deal and nobody stops. The small enamel plates and the commemorative marbles are the densest free history in the city.
• Look at the ground. Bronze markers set into pavements trace the line of the Philippe Auguste wall and other vanished structures.
• Look above the shopfronts. Ground floors get replaced every decade; the three storeys above them often have not changed since they were built.
• Walk the same street twice, once on each side. You see entirely different buildings, because you can only see a facade properly from across the road.

Or ask the building directly

This is the problem Globo was built for. Point your camera at whatever you are standing in front of — a monument or a nondescript facade — and it identifies the place and tells you its story, with an audio version you can listen to while you keep walking. The plaques are excellent; they are just not on every building.