Hi Ebi-Il
Well, I tried to tanslate into rules the understanding of the World of very ancient Mesopotamian (at least as I understood it). Everything is granted (or caused) by the gods and "magic" is not a kind of manipulation of natural forces like in classical fantasy magic. All surnatural deed are obtained through proper rituals and sacrifices, taking the piety into account. No "battle magic", no "divine magic" with POW sacrifices: sacrifices are very real, like food, animal or money, just as the gods are very real, living in temples as statues. All the rituals are written on tabletts: mesopotamian "magic" is a science, as they understood it, requiring years of studies and of course to know how to read Sumerian. Almost all the "magicians" are actually priests and scientists, which may sound weird in the XXIst century (AD!).
Divine help is gained in temples, every God helping in his domain at a level depending on the piety and the amount of sacrifices.
A big part of "magic" is the exorcism, which is not seen as a magical power but instead as a science of chasing demons away from the victim, again with rituals and sacrifices: almost all the troubles and diseases are caused by demons sent by the gods, who also teached the humans how to chase them. Any exorcist may deal with any demon, like a doctor can try to cure any disease. Exorcists may call demons for their proper use, but not without danger.
Sumerian magicians are like demons summoners. This recalls the older times of Sumer when all the demons and rituals hadn't been recorded on the tablets : the science of exorcism was at the begining and much more limited than later.
There are also a special chapters for necromancy and divination.
Note that I wrote this setting for Sumer and Akkad in the 3rd millenium, not for Babylon or later empires, even if many things stayed relatively constant in time.