The artist states that over 9,000 bodies were scattered on the field to generate multiple layers of corpses. The team was able to make intelligent use of instancing to keep render times low as the opening shot was several hundred frames long.
“Characters ranged from 500k to 900k polys, depending on their outfit and hairstyle. The bodies were posed by the animation team and then their clothes and hair were simulated into place and touched up in ZBrush,” added Grant Miller.
Make sure to read the interview here.