The Undead Army's assault was indeed full of aggression and momentum.
Gazing from above the city wall, the Undead Creatures resembled an earth-shattering, pitch-black dye running on an artist's canvas. Everything on the surface was concealed by the dense, neat, and frightening movements. If they were Humans, perhaps the most elite of soldiers couldn't charge forward as neatly as them. Even though flames were spreading around them and explosions had blasted them away, their pace was still consistent, unified, without the slightest confusion. It was this display from them that the Humans realized clearly that what they were facing was an entirely different existence.
They weren't Humans.