During the revolution, no one had an accurate map of Paris.

This is what made the barricade such an effective tool. People could throw up a few barricades and quite effectively defend a neighbourhood.

When the army showed up they had to channel through narrow unfamiliar streets.

If the tide turned against the people, they often managed to escape through a little known back alley.

The "Grande Boulevards" may look majestic, but they are also military roads. They make it easier to move troops within the city.