Mauru had been in charge of keeping the battlement guards from attacking the Alterans entering through the bridge. However, Miss Althea realized they were needed more on ground level so they devised a way to lessen the labor requirement in the battlement.
What they did was to use the bodies of the guards taken down to block the way of the oncoming ones.
This way, they'd have to climb over half-dead or dead bodies to get to them, which was in no way easy. It was more likely they'd slip down.
Their walls were so thin that it wasn't even difficult to do so. They simply had to lay them down in whatever way, arranging it in a way the short 'wall' wouldn't roll in their direction instead.
There was also Miss Althea who assisted them. She would shoot people skillfully and let them fall right at the surface to cause an obstacle.