Byzantine Empire
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Kiev, but relations were not always friendly. The most serious conflict between the two powers was the war of 968–971 in Bulgaria, but several Rus' raiding expeditions against the Byzantine cities of the Black Sea coast and Constantinople itself are also recorded. Although most were repulsed, they were concluded by trade treaties that were generally favourable to the Rus'.
Rus'-Byzantine relations became closer following the marriage of the porphyrogenita Anna to Vladimir the Great, and the subsequent Christianization of the Rus': Byzantine priests, architects and artists were invited to work on numerous cathedrals and churches around Rus', expanding Byzantine cultural influence even further. Numerous Rus' served in the Byzantine army as mercenaries, most notably as the famous Varangian Guard.
The Byzantine Empire then stretched from Armenia in the east to Calabria in Southern Italy in the west. Many successes had been achieved, ranging from the conquest of Bulgaria, to the annexation of parts of Georgia and Armenia, to the total annihilation of an invading force of Egyptians outside Antioch. Yet even these victories were not enough; Basil considered the continued Arab occupation of Sicily to be an outrage. Accordingly, he planned to reconquer the island, which had belonged to the Roman world since the First Punic War. However, his death in 1025 put an end to the project.
The eleventh century was also momentous for its religious events. In 1054, relations between the Eastern and Western traditions within the Christian Church reached a terminal crisis. Although there was a formal declaration of institutional separation, on 16 July, when three papal legates entered the Hagia Sophia during Divine Liturgy on a Saturday afternoon and placed a bull of excommunication on the altar, the so-called Great Schism was actually the culmination of centuries of gradual separation.
Crisis and fragmentation
Byzantium soon fell into a period of difficulties, caused to a large extent by the undermining of the theme system and the neglect of the military. Nikephoros II (963–969), John Tzimiskes and Basil II changed the military divisions (τάγματα, tagmata) from a rapid response, primarily defensive, citizen army into a professional, campaigning army increasingly manned by mercenaries. Mercenaries, however, were expensive and as
The very brief first coinage of the Thessaloniki mint, which Alexios opened as he passed through in September 1081 on his way to confront the invading Normans under Robert Guiscard.