I thought you might be interested to know that I've just published a book called The Roman Revolution. This is about the Roman Empire in the third century when Rome was truly revolutionized and ended up as a Christian monarchy. This was the origin of the Byzantine Empire, and so if you're interested in the Crusades, you might well enjoy this much earlier time in history which was so formative for both Byzantium and the Crusades. Here is the link to the book on Amazon US. One click and you're there! Hope you enjoy it!