Essentially, the Emperor would protect the Eastern Christian Church and manage the administration of the Church by presiding over the Ecumenical Councils and appointing Patriarchs and set the territorial boundaries for their jurisdiction. Therefore, there was no separation of Church and State, thereby forming a single power structure from the two entities.
The early survival of the Byzantine Empire was made possible through its naval force. The sea became vital to the existence of the empire in the east, which many historians refer to as the maritime empire. Greek fire was a bomb used by the Byzantine Empire, specifically by the navy as it could continue burning while floating on the water. This was an early technological advantage and was responsible for many military Byzantine victories. During this early period, Heraclius became Byzantine Emperor from 610 AD to 641 AD. The empire was being threatened on many fronts, but Heraclius immediately took charge of the campaign against the Sassanid Empire of Persia. This war was fought from 602 AD through 628 AD and was the final and most devastating of the series of wars fought between the Eastern Romans and the Sassanid's. Although the Persians proved to be quite successful in the first ten years of the war, ascension of the throne by Heraclius sealed their fate. Despite initial setbacks, Heraclius' campaigns in Persian lands from 622 AD to 626 AD forced the Persians onto the defensive and allowing Heraclius' forces to gain strength. Allied with the Avars, the Persians made a final attempt to take Constantinople in 626, but were defeated there. In 627 AD at the Battle of Nineveh, Heraclius invaded the heartland of the Persians and forced them to initiate the peace process. Soon after this victory, however, Heraclius was faced with the Muslim conquests that began with the Islamic prophet Muhammad. The Muslim conquests brought the collapse of the Sassanid Empire, which was a great territorial loss for the Byzantine Empire.
