Latest read (audio), vol 5 of Decline and Fall of the Roman Empire (1776) by Edward Gibbon; Law after the Roman Empire, Greek emperors of Constantinople, Eutyches' human Christ vs. Nestorius' divine Christ. This Massive work takes on a different character as Europe & The Church take shape. #BookSky
The strangest thing about Gibbon's Decline and Fall of The Roman Empire is that, in its thousands of pages, he almost never mentions a date. You only know what year an event is taking place in if you are familiar with various historical cues.
But I still feel this may be the richest resource for political world building for fantasy and sword and sorcery writers you could hope to find.