Diplomacy
Byzantine Empire

The key challenge to the Byzantine Empire was to maintain a set of relations between itself and its sundry neighbors, including the Georgians, Iberians, the Germanic peoples, the Bulgars, the Slavs, the Armenians, the Huns, the Avars, the Franks, the Lombards, and the Arabs, that embodied and so maintained its imperial status. All these neighbors lacked a key resource that Byzantium had taken over from Rome, namely a formalized legal structure. When they set about forging formal political institutions, they were dependent on the empire. Whereas classical writers are fond of making a sharp distinction between peace and war, for the Byzantines diplomacy was a form of war by other means. With a regular army of 120,000–140,000 men after the losses of the 7th century, the empire's security depended on activist diplomacy.

Byzantium's " Bureau of Barbarians " was the first foreign intelligence agency, gathering information on the empire's rivals from every imaginable source. While on the surface a protocol office—its main duty was to ensure foreign envoys were properly cared for and received sufficient state funds for their maintenance, and it kept all the official translators—it clearly had a security function as well. On Strategy, from the 6th century, offers advice about foreign embassies: " who are sent to us should be received honorably and generously, for everyone holds envoys in high esteem. Their attendants, however, should be kept under surveillance to keep them from obtaining any information by asking questions of our people."
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