The Byzantine Empire had a thousand year history that requires proper attention to understand Orthodox and Catholic Christianity, the Crusades and Islam.
In the spring of 2003, I took my last undergraduate history course, an elective on the history of the Byzantine Empire, taught by Maria Mavroudi. The class was excellent, and against the backdrop of the occupation of Iraq that occured in March of that year, a lesson in the rhyming patterns of history.
Professor Mavroudi was awarded a MacArthur grant in 2004 to further her study of the two-way exchange that occurred between the Byzantine and Islamic cultures.
The book we used in the class was The History of the Byzantine State by George Ostrogorsky. Worth a read.