Attacks from the Rear!!
Sad for them, they were too dense and too many that they were temporarily unaware of the impending doom approaching them from the rear.
At this time, everyone was just focused on getting to the various access points and entering that damned territory!
Monsters tended to target the gates—the weak spots. However, humans had brains so they naturally didn't focus their attention on the gates, which were usually the best-equipped sections of the walls.
Rather, they would focus on random spots where—ideally—there were the least amount of guards. This was easier to find in other territories because most territories couldn't afford this many sentries.
Still, they could make up for it by their sheer numbers! This number alone was a lot more than the total population of Alterra.
Not even including the slaves they idiotically let inside, Alterrans were already severely outnumbered!