Indeed, by the evening it becomes obvious that Courfeyrac is not defending this fortress alone. As soon as the ramparts solidify, a veritable army of fighters take their stations atop it, shadowed figures standing silent vigil to watch for intruders. They are prepared to brace the cold in their assortment of parkas and blankets--one even seems to have a tent wrapped around him--and prepared for battle with the piles of snowballs lined at their feet. Sunset carves their features into the very structure of the barricade itself.

That's probably because they are, in fact, part of the barricade. People approaching from a different angle will probably realize pretty quickly that someone's just made a bunch of snowmen and piled them atop the walls. The person who made them is likely also the one that just pelted you with a snowball. People who are helping to build the fortress are not safe from this.

If nothing else, Gary has discovered that the snowmen make for great shields to hide behind while he listens to the cries of dismay and prepares another snowball.