Polybius should be praised for his sagacity, for although his perspicacity failed him with regards to the Pontus and the eventual transformation of the Euxines into a freshwater lake, it was spot on in his expatiation on Byzantium. He was able to grasp not only the strategic value of this place, but also what ultimately proved to be its demise.
The location of Byzantium afforded it control over this vital bridge between East and West, and even the currents would force travellers to make way to Byzantium. Constantine the Great was able to assess the potential in this fishing town, moving the capital of the world here, though his decision to extirpate the soul of the Empire and transplant it to a backwater region was a decision borne, to a great extent, from necessity.
Unfortunately Constantine was unable to grasp the potential problems of this region of the world: the swarming sea of barbaroi to the northeast of it. Polybius was able to discern that threat, arguing that Byzantium ran the risk of being sieged constantly by wave after wave of barbarians, especially if the city chose to appease, through bribery, the wrath of the tribal lords then to quell their rage by spilling their blood on the battlefield.
Constantine divided the Empire’s forces at a time when it needed to be united — as the Romans learnt during the Hannibalic invasion of the Italic peninsula — choosing to delay the fall to a later time: 1453. Though I would agree that the Eastern Roman Empire was not the Roman Empire neither in essence nor substance. It was a Greek empire in every sense of the word; something altogether different and unique.