The continuing interest of Byzantium in Venice cannot be explained solely in terms of the emperors' claims to universal imperium. The bubble of Justinian's imperialistic dream had been pricked first by the Lombards and then by the Franks. Sicily, parts of south Italy and some of the Dalmatian coast were still in Byzantine control at the beginning of the ninth century. Venice was a remote corner, isolated except by sea. It might be argued that Byzantine interests there had been preserved by the accident of the clash between the empires of east and west about 800. The settlement that came out of that confrontation laid certain mutual obligations on Venetians and Byzantines alike. Thereafter the Emperors in Constantinople expected that the Venetians would do their duty by sending ships to reinforce the Byzantine navy in south Italy when required; their expectations were often realised. But there were other factors that connected the interests of Byzantium and Venice.

The earliest Venetian chroniclers were well informed about Byzantine affairs, though they tended to interpret them in their own way. John the Deacon has as much to say about the Emperors of Constantinople and their families as he has about the Lombard or Frankish kings. Constantine Porphyrogenitus, on the other hand, who was writing half a century earlier, knew a surprising amount about the history and topography of Venice. He was aware that its inhabitants, originally called Enetikoi, had at first lived on the mainland in Concordia and other cities before they crossed over to the islands.