Byzantine diplomacy concerns the principles, methods, mechanisms, ideals, and techniques that the Byzantine Empire espoused and used in order to negotiate with other states and to promote the goals of its foreign policy. The conventional view of diplomacy is one of negotiation and compromise leading to a settlement of differences.
In protecting the state against the barbarians who surrounded it, diplomacy was a weapon as important in the eyes of the Byzantine government as soldiers or fortifications. The peace on the frontiers was maintained not only by strong military defenses, but by more or less skilful management of the frontier peoples. In the later Empire this kind of diplomacy; which may be defined as the science of managing the barbarians, was practiced as a fine art; its full development was due to Justinian.
Byzantium produced the first professional diplomats. They were issued written instructions and were enjoined to be polite, to entertain as lavishly as funds permitted, and to sell Byzantine wares to lower their costs and encourage trade.
Since it was impossible for the Empire to defeat every one of its enemies militarily, diplomacy became the primary instrument of strategy.
After the fall of the Western Roman Empire, many diplomatic traditions disappeared. Diplomacy continued to thrive, however, in the eastern Roman Empire—also known as the Byzantine Empire or Byzantium. Emperor Constantine XI Palaiologos' diplomatic relations with other powers depended heavily upon his personal relationships with foreign elites and dignitaries.
He developed these throughout his tenure as despot of the Morea and while Roman emperor. He relied upon these relationships, rather than upon bureaucratic channels, because the Byzantine bureaucracy deteriorated along with the state. The emperor also relied heavily upon the personal relationships between members of his court and foreigners within the imperial capital. When Constantine and his court possessed direct, personal relationships with influential foreigners, relations with their home states improved.
In addition, the Byzantines created streamlined, coherent foreign policies toward those states. When the emperor or his court did not possess significant personal relationships with foreign elites, relations with those states suffered. Also, Constantine and his advisors could not create coherent foreign policies toward them.
Another mode of winning influence was to marry barbarian princes to Roman wives, and rear their sons in the luxury of the palace. Dissatisfied pretenders, defeated candidates for kingship, were welcomed at Constantinople. Thus there were generally some princes, thoroughly under Byzantine influence, who at a favorable opportunity could be imposed on their compatriots. Throughout Justinian's reign there was a constant influx of foreign potentates to Constantinople, and he overwhelmed them with attentions, pompous ceremonies and valuable presents.
A further diplomatic ploy was the use of surrogates. The Byzantines hated the expense of war and could hardly afford the cost in human life. Often they would get others to fight for them. If the Bulgars were troublesome, the Russians were called in. If the Russians were troublesome the Patzinaks (a central Asian tribe) were summoned. The Cumans and Uzes acted as checks on the Patzinaks and so on. The Byzantines almost always had an ally to the geographic rear of a potential enemy.