User blog comment:ImperiexSeed/The oldest being, archangel or leviathan?/@comment-184.77.255.73-20120506183558/@comment-1509826-20120507230237

He's so strong, because his powers were being channeled into him, by Lucifer himself, he was being given the archangels power (not all of it but most) thats why he only got so strong after lucifer rose.

And yeah, Roman is strong, he's stronger than angels, he would probably, on a good day, be able to kill a lower archangel, and maybe if he was lucky and managed to sneak up behind them, kill a higher one. But he couldn't kill Michael, Michael is the strongest creation there is, nothing is as strong as him, only stronger and weaker.