<P> After the fall of Rome, the key challenge to the Empire was to maintain a set of relations between itself and its neighbours . When these nations set about forging formal political institutions, they often modelled themselves on Constantinople . Byzantine diplomacy soon managed to draw its neighbours into a network of international and inter-state relations . This network revolved around treaty making, and included the welcoming of the new ruler into the family of kings, and the assimilation of Byzantine social attitudes, values and institutions . Whereas classical writers are fond of making ethical and legal distinctions between peace and war, Byzantines regarded diplomacy as a form of war by other means . For example, a Bulgarian threat could be countered by providing money to the Kievan Rus' . </P> <P> Diplomacy in the era was understood to have an intelligence - gathering function on top of its pure political function . The Bureau of Barbarians in Constantinople handled matters of protocol and record keeping for any issues related to the "barbarians", and thus had, perhaps, a basic intelligence function itself . John B. Bury believed that the office exercised supervision over all foreigners visiting Constantinople, and that they were under the supervision of the Logothetes tou dromou . 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 probably had a security function as well . </P> <P> Byzantines availed themselves of a number of diplomatic practices . For example, embassies to the capital would often stay on for years . A member of other royal houses would routinely be requested to stay on in Constantinople, not only as a potential hostage, but also as a useful pawn in case political conditions where he came from changed . Another key practice was to overwhelm visitors by sumptuous displays . According to Dimitri Obolensky, the preservation of the ancient civilisation in Europe was due to the skill and resourcefulness of Byzantine diplomacy, which remains one of Byzantium's lasting contributions to the history of Europe . </P> <P> For most of its history, the Byzantine Empire did not know or use heraldry in the West European sense . Various emblems (Greek: σημεία, sēmeia; sing . σημείον, sēmeion) were used in official occasions and for military purposes, such as banners or shields displaying various motifs such as the cross or the labarum . The use of the cross, and of images of Christ, the Virgin Mary and various saints is also attested on seals of officials, but these were personal rather than family emblems . </P>

When did the byzantine empire reached the height of its power