The Shadow of the Lion is an alternate history/historical fantasy novel set primarily in the Republic of Venice in the 1530s. It is a part of the Heirs of Alexandria series. The book was written by Mercedes Lackey, Eric Flint and Dave Freer and combines elements from the styles of all three authors, such as Lackey's approach to tolerance and magic and Flint's sense of history alteration. The book was published in various e-book formats in the Baen Free Library and on Baen CD #01 (Honorverse).[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. She continued her correspondence with John and St. Augustine, which eventually led to the modern (1530s) divisions of the Church. The Library was a great storehouse of magical knowledge—the inference being that the information was lost to us in this universe when the Library was destroyed. 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. Notably, the clergy utilize elemental magic.
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. The Petrines are noted for taking a mediative role in politics and a more tolerant attitude to other faiths.
Most of central and northern Europe follow the Pauline creed (named for St. Paul and based on the writings of St. Augustine). The Paulines are recognized for a general intolerance to all non-Christians, though some members of the Church are more politic about it than others. There is no official head of the Pauline church, though the Holy Roman Emperor is the "Bulwark of the Faith".