Back when I was more literate, 30 years ago, I researched the history behind this book. The main points are factually accurate. This should be required reading for all Christians who think that the religious takeover of the 4th century was benign or inevitable.
I didn't want to finish this novel because I didn't want the characters to be out of my life: can't recommend it more highly than that. This is what historical fiction should be. I'd never read Vidal before; now I've already ordered another of his works.