I was in Paris last month and was really struck by the huge police presence, particularly around historic sites.
One afternoon about 15:00, my wife and I witnessed a brawl of four or five men at the park adjacent to the Eiffel Tower. It was immediately broken up by about a dozen police which came running from several directions.
There were at least a dozen police in full SWAT gear near the Arc de Triomphe. Many of the police officers had assault rifles. The Champs-Élysées was barricaded on both ends and every side with police checkpoints at every possible entrance of its entire 2km length. We were denied entrance because I had a bottle of 2014 Rothchild's Mouton Cadet. Who would have thought wine was contraband in Paris.
The #1 Metro line, which runs under the Champs-Élysées, was closed. As a result, connecting lines were extremely overcrowded.
The whole experience was very disappointing. But at least my wife and I survived unscathed.