Paris was still a walled city going into the twentieth century - it was enclosed by seven successive walls. Ironically, virtually nothing remains of the newer walls, while numerous vestiges of the walls of Phillipe Auguste (built 1190-1213) can be found all around the center of the city. The few images here (around a map of the old walls superimposed, very approximately, on a modern map) are only some of what remains (though many of the others are hidden in courtyards, restaurant cellars, etc.)
Again in French, this article provides a good history of the wall.
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