[1][2] In our own universe, Hypatia of Alexandria was killed for her non-Christian views, shortly before the destruction of the Library by an angry mob.
In this universe, Hypatia was converted to Christianity by John Chrysostom, and stopped the mob from destroying the Library.
In this universe, while magic is not commonplace its existence is no secret to the general populace and is practiced by those with the inborn power and/or discipline to use it.
Led by the Grand Metropolitan in Rome, the Petrine branch of the Church (named for St. Peter and built on the teachings of Hypatia and Chrysostum) is the creed of choice in Italy and Spain, with a relatively large following in Aquitaine.
Most of central and northern Europe follow the Pauline creed (named for St. Paul and based on the writings of St. Augustine).