Impressed by the fact that Byzantium lasted more than any other state in history, although always surrounded by enemies and being constantly under attack, the strategist and historian Edward Luttwak for more that two decades studied Byzantium and wrote a book called The Grand Strategy of the Byzantine Empire. His study of Byzantium made Luttwak understand that the success of the Byzantine Empire was due to two factors mainly: the strategic intelligence of the Byzantines, and their cultural strength. In this interview Luttwak speaks about Byzantine studies and about his findings regarding Byzantine strategy. Besides his merits as a scholar, Luttwak is also a great speaker, you will enjoy his company.
Cf. Ed. Luttwak’s The Grand Strategy of the Byzantine Empire, at Amazon
Cf. Walter Emil Kaegi, Jr., Some Thoughts on Byzantine Military Strategy