User blog comment:ImperiexSeed/The oldest being, archangel or leviathan?/@comment-76.95.86.12-20120519182004/@comment-31.53.226.53-20120520094946

in response to the comments above, an archangels blade was used on castiel because it was the same one they threw at raphael. keeping michael and lucifer in the cage was proably more a problem as they would A: want cas dead for replacing their father, B: they would probably roast the planet in revenge. Lucifers's cage can be open with the horseman rings or 66 seals at any time. purgatory can only be open at a lunar eclipse with virgin blood and the blood of a creature from purgatory ( not easy to obtain), so it can be argued its harder to free leviathans than it is to free lucifer. And yes but without any of their angelic powers an archangel is about as strong as a alpha and edgar would have easily killed the alpha. if leviathans cannot be harmed by angelic powers then the archangels are defenless and would be chomped or poisoned by the black goo. This would explain why god didn't just command michael to destroy them after he made michael, incase there was a risk michael would get hurt. also edgar has proved leviathans can kill multiple angels as the leviathans killed all of castiels garrison.