One of my favorite historical subjects to study is the Byzantine Empire. It is quite an interesting period of Church history. There is a great website that offers online publications on Byzantine history called Dumbarton Oaks. They have free online publications on Byzantine art, monasticism, the crusades, churches and the list goes on. It is a great resource for any scholarly research on the subject. They also have some great books for sale as well. You can add this to your research list.