I know in the movie 'Gone With the Wind' there were scenes (when they show the multitude of wounded) where they used dummies to cut down the number of extras needed. Does anyone know if anything was done in this movie to trick the audience into believing there were more people than actually hired or was it a cast of thousands?
'What do we do now?' - The Candidate
Most of them were real people, but they did use matte painting on glass for many of the wide shots that showed things like the Paris city landscape and the Place de la Revolution where the guillotine stood. Some of the people in those shots may have been painted, though they'd be in the back of the shot where you wouldn't notice that they weren't moving.
But for the most part they simply hired a ton of extras for the massive crowd shots.