Promethean Knights are Forerunner constructs made of an unknown alloy and hardlight that are driven by composed souls, or essences. Being composed involves being scanned extremely deeply by entangled sympathies.If your neural complexity resonates correctly with the Composer, your neural pathways are digitally mapped. This process involves your incineration and death. The Knights were very effective against the Flood. The only thing that prevented them from making headway was the fact they were introduced so late into the war, and that there weren't enough of them.