The Heirs of Alexandria series, by Mercedes Lackey, Eric Flint and Dave Freer. These are historical fantasies (c.1440 AD) set in an alternate universe. They are mostly set in Venice or the Eastern Mediterranean. The break point is the death of Hypatia in 415 AD; in this universe she survived and became a colleague of John Chrystostom, founding the Hypatian Order. The other thing is that magic and magical beings exist. See https://en.wikipedia.org/wiki/Heirs_of_Alexandria_series for more information.

1 Heirs of Alexandria, by Mercedes Lackey, Eric Flint and Dave Freer​
Set in 1437+1438 in Venice. Orphan half-brothers Marco and Benito Valdosta acquire a protector and become involved in the politics of the city, saving it from a threat posed by Jagellion, Grand Duke of Lithuania (who has been taken over by a demon). They become involved with Manfred of Brittany, second heir to the Holy Roman Emperor Charles Frederick Hohenstauffen, and his Vinlander bodyguard, Eric Haakonson, who foils a plot by a religious order, the Servants of the Trinity, and their secular arm, the Knights of the Trinity.

2 This Rough Magic, by Mercedes Lackey, Eric Flint and Dave Freer​
Set in 1438-1439 in Venice & Corfu. Marco stays behind in Venice, Benito is exiled to Corfu (we won't mention why). Manfred and Erik head to Jerusalem. King Emeric of Hungary decides to invade Corfu with assistance from his long-lved 'aunt', Elizabeth Bathory, and Jagellion..

2.5 A Mankind Witch, by Dave Freer​
Set in 1438-1439 in Telemark (one of the Scandinavian kingdoms). A Barbary corsair on a plundering expedition to the north is shipwrecked and taken as a thrall in Telemark. He is given to the Princess Signy, who is under the subjection of her stepmother and half-brother (who is now the king).

3 Much Fall of Blood, by Mercedes Lackey, Eric Flint and Dave Freer​
Set in 1540-1541 in the Balkans and the Eurasian steppe. Following the invasion of Corfu, Benito is made acting governor and starts making feelers to Iskander Beg. Manfred and Eric continue their interrupted pilgrimage to Jerusalem, and end up escorting a Mongol ambassador from the Ilkhanate to their cousins in the Golden Horde. In Hungary, Elizabeth Bathory frees Vlad of Valachia from King Emeric - she has designs on him. Vlad escapes and falls in with a shapeshifter pack who take him back to Valachia where he raises the flag of rebellion.

4 Burdens of the Dead, by Mercedes Lackey, Eric Flint and Dave Freer​
Set in 1540-1541 in Constantinople and the Black Sea. Benito leads a fleet to invade the Byzantine Empire in order to depose Alexius (who has gone too far dealing with foreigners). The Ilkhanate are unhappy with the Baitani who have been fomenting trouble in the Black Sea.

I very much like this series; it's the sort of fantasy I enjoy. As #5 is due out later this year, I thought it best to refresh my memory (although I probably won't get it until the paperback comes out...) . Somewhat reminiscent of the Merovingen Nights sharecrop (especially the first in the series), but fantasy rather than SF. Each book is a standalone, but it helps to have read the previous to understand the politics (apart from A Mankind Witch which is a true-standalone). I do like these - they're an epic romp through early renaissance politics - it's fun spotting the historical background and wondering what could have happened to so-and-so. The glaring omission is the Medici in Florence; we see the Del Estes of Ferrara, the Visconti of Milan, and Carlo Sforza, but no mention of the Medici (Florence is mentioned, but doesn't seem to be one of the great city states in this version of history). The other thing is that there seems to be some conflation of history; partly because of the different timeline and partly because of the old magical beings still extant.

Recommended. (Similar are: The Kushiel series by Jacqueline Carey although this version has Christianity, and also the Instrumentalities of the Night series by Glen Cook. The Mongol Empire is similar to the Assassini series by Jon Courtney Grimwood.)

Hard to sustain interest. Less like a story and more like an anthology.. ( )