D. Zakythinos’ “Byzantine History” is one of the best histories of Byzantium, if not the best so far, (not translated in English at the moment). This doesn’t mean that we should agree in everything there written. One of such disagreements that I have is about the start of Byzantium. It is known that Byzantium is just a name later given to the Eastern part of the Roman Empire, a name Byzantines themselves never used. Therefore, we should speak just about the Roman Empire, as Gibbon did, which at some point in time loses its western part to the teutonic kingdoms.
On the other hand, we feel that there is a justification in distinguishing between the older and the byzantine part of the Roman empire. A feeling may provide a stimulus to thinking, but we can not establish a certain distinction upon feeling. Our first task then, would be to find the distintive feature of what we call “Byzantium”.
Among the proposed dates for the start of the specifically Byzantine history, Zakythinos prefers 395, when the empire was divided in the Eastern and the Western part, dismissing 324 or 330 or even the date of the First Ecumenical Council, because, as he writes, “the period between 324 and 395, however crucial might have been (for the further developments in the Roman world), belongs organically to the history of the united Roman state”, while from 395 and afterwards, “the eastern state distances itself from the West and gradually proceeds to its own characteristic forms”.
If we accept this, then I don’t see why we shouldn’t accept the rise of Diocletian as the essential start of the Byzantine history. Zakythinos acknowledges that the rise of Diocletian is a reasonable point, but he refuses to accept it because it ignores the principal characteristic of Byzantium, i.e. Christianity. This way Zakythinos uses two different criteria, and in the same time he denies both of them!
If indeed Christianity is the main characteristic of Byzantium, the one we should use to determine, even conventionally, the start of its history, then 395 can not be accepted. I think we are right to say that Byzantium starts (or, that the Roman empire starts to become the Byzantine empire) when persecutions of Christians stop and Christianity is recognised as the official religion of the empire. Since this transition is identified with the foundation of Constantinople, I believe the most convenient date for the start of the Byzantine history would be the foundation of Constantinople (324 or 330).
We must also not forget that during the 4th century, precisely in the East, we have the foundations of Christian theology, with Athanasius and the Cappadocian Fathers, even the great development of organised Christian monasticism and the first Ecumenical Synods of Christianity – where the Roman emperor himself was involved! Although mindful of the whole history of Byzantium, Zakythinos is mistaken by the greater importance that he places on the narrow political side. This side may not be yet, in the 4th century, “Byzantine”, but the main causes leading to the transformation and new character of the Roman Empire are already at play here, in this century.