Who would have guessed that the Louvre underground holds the vestiges of a fortress built by King Philippe Auguste in the 12th century to defend Paris? Who could have imagined that we would still see, four centuries after its destruction, the Great Tower of the Louvre, a symbol of the State? Who would have thought that one day we could walk in the moat, once filled with water, that encircled the fortress? And along the surrounding wall that protected the city? The medieval Louvre is alive and well, as it invites “art researchers” on an extraordinary tour.