Why did the Paris crowd rush to their city gates every evening, and whose gates was their favorite one to visit?

The Paris crowd rushed to the gates late every afternoon to see who would attempt to flee the city. The people favored the West Gate, where Sergeant Bibot was reputed to have an uncanny knack for sniffing out aristocrats in disguise.

But they were nearly always caught at the barricades, Sergeant Bibot especially at the West Gate had a wonderful nose for scenting an aristo in the most perfect disguise. Then, of course, the fun began. Bibot would look at his prey as a cat looks upon the mouse, play with him, sometimes for quite a quarter of an hour, pretend to be hoodwinked by the disguise, by the wigs and other bits of theatrical make-up which hid the identity of a ci-devant noble marquise or count.
Oh! Bibot had a keen sense of humour, and it was well worth hanging round that West Barricade, in order to see him catch an aristo in the very act of trying to flee from the vengeance of the people.
Sometimes Bibot would let his prey actually out by the gates, allowing him to think for the space of two minutes at least that he really had escaped out of Paris, and might even manage to reach the coast of England in safety, but Bibot would let the unfortunate wretch walk about ten metres towards the open country, then he would send two men after him and bring him back, stripped of his disguise.