The oath

Well during a ritual, i asked Astaroth about the slavery of demons in certain legions, she answered with that, The Oath of Helios is the one i might be asking about. In ancient times there was an oath that binded captured demons or angels toa legion for the the amount of time their punishment existed. However about the rest she did not tell me so can E.A. or anyone else tell me what i am missing about this subject?