Between 850 and 1100, the Empire developed a mixed relationship with the new state of the Kievan Rus', which had emerged to the north across the Black Sea. This relationship had long-lasting repercussions in the history of the East Slavs, and the Empire quickly became the main trading and cultural partner for Kiev. The Rus' launched their first attack against Constantinople in 860, pillaging the suburbs of the city. In 941, they appeared on the Asian shore of the Bosphorus, but this time they were crushed, an indication of the improvements in the Byzantine military position after 907, when only diplomacy had been able to push back the invaders. Basil II could not ignore the emerging power of the Rus', and, following the example of his predecessors, he used religion as a means for achieving political purposes. Rus'–Byzantine relations became closer following the marriage of Anna Porphyrogeneta to Vladimir the Great in 988, and the subsequent Christianisation 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, while numerous Rus' served in the Byzantine army as mercenaries, most notably as the famous Varangian Guard.