If you are interested there is a three part series of books by an englishman named Norwhich. Byzantium, The Ris, Apogee, and Fall. I have them and have read them several times. Very good reading. The author tells a good story and it does not come across as dry.
There is an alternative history book by Tutrtledove of a Byzantine empire that never fell - Mohammed instead of being a Muslim prophet became a Byzantine holy man, etc.