Fun fact, the reason the Louvre has such tight security now isn't just because the Mona Lisa was once stolen, but the humiliating manner in which it was done so. The building is massive but only had some 200 guards, and the painting was a bit less popular before it was stolen and got a bunch of international publicity, so the thief was quite literally able to just walk up, take it, and book it before anyone could notice.

I'm missing some details here and there, but that's basically the long and short of it.

This is what happens when you don't hire a pro-thief to steal valuable art...