Outside the city, in a perfect circle around it, there were about three million beasts—just souls, of course. Of these three million, only one million were souls that had already died and were eternally enslaved in that place. The other two million were summoned just to clear the way.
Alm and Bruno quickly understood the four kings' plan. The regular soldiers would attack all at once, forcing them to deal with them, while the truly powerful ones would try to deal as much damage as possible all at once. The goal was to drain as much of their energy as they could.
The kings didn't expect to defeat them quickly, so they didn't come in person. They would just keep up the constant pressure, not giving them time to recover.
The kings weren't stupid and surely noticed that the twenty had been removed from their arrangement. But they didn't care. This was a divine Dao; to accomplish that, they imagined it must have burned a lot of divine soul power.