Which is the best audio guide to the Louvre?

These stones used to face a moat. There was no glass pyramid above them. There was no museum. This was the edge of a fortress.

King Philippe Auguste began building the first Louvre around 1190, on the western approach to Paris. The threat came from beyond the city. A walled castle could guard a vulnerable side and store weapons. It was not first planned as a comfortable home for a king. Inside its rectangular walls stood a huge round keep called the Grosse Tour, the Big Tower. Around the outside ran the moat. The buried masonry in this room belongs to that earlier building, not to a gallery invented to look medieval.

The castle did not keep the same job for long. As Paris grew, new defenses carried the city's edge farther west. The fortress found itself inside the city it had once protected from outside. Royal rooms took over a place that had been built for soldiers and stores. Later kings wanted light, ceremony and space. François I had the old keep pulled down in the sixteenth century. The Renaissance palace rose where the defensive stone had stood. Its walls hid what had been here before.

The buried part waited through still more changes. The palace became a museum. New wings surrounded old courtyards. In the late twentieth century, the Grand Louvre project brought excavations into the heart of the building. The old foundations came into view again. Here the museum did not need to acquire an object from another country or another century. Its own earlier body was underfoot.

Look at the weight of the masonry. A moat is usually imagined as water or an empty trench. What survives here is the wall it defended. It makes the word 'Louvre' feel different. Upstairs, it can mean paintings, crowds and long corridors. Down here, it once meant a barrier on the edge of a city. The same site changed from weapon store to royal residence to public museum without ever quite letting go of its first shape.

There is a temptation to call these ruins the start of the museum. The people who set the stones would not have recognized that future. They were making a place that could resist an attack. The building later became useful for almost the opposite purpose: opening its rooms to strangers. A public walk through the old moat is possible because its first job is long over.

The moat is no longer outside the Louvre. It is a room inside it.