Crossing the road to get to Paris's famous Arc de Triomphe is not for the feint of heart. With 12 avenues converging to form up to 10 lanes of traffic going in an endless circle, trying to cross on foot probably means near certain death. That is, unless you have your own portable crosswalk.
There are no permanent pedestrian crossings across the circle, so this flashmob from the French action theater group X TNT decided to create their own providing street level access to the monument. The members strode confidently out into the place carrying white boards that they dropped onto the road to create the crosswalk, then a bunch of people were able to cross before the gendarmerie arrived to break up the party.
Normally people can access the Arc de Triomphe using an underground passage, but that's not much help for the elderly or people in wheelchairs. I guess the X TNT folks were just trying to make a point.
Check out the video to see the X TNT flashmob in action.