The history of Byzantium in this period cannot be divorced from that of Bulgaria, with which it shared borders for over 1000 kilometres. A contemporary encomiast in Bulgaria had compared Symeon with the founder of the library in Alexandria, Ptolemy. According to Byzantine chronicles, Symeon was provoked into war by the arbitrary manipulation of Bulgarian trade in Constantinople, and by the raising of customs dues. There were undeniably strains in Byzantino-Bulgarian relations after Symeon's massive show of force in 913. The sequence of events which brought Sviatoslav to the Balkans is controversial, because our main sources show discrepancies. At the same time, Bulgarian forces occupied much of Byzantine Thrace. Tomislav, however, inflicted a heavy defeat on the Bulgarians and, in a sense, vindicated Symeon's decision to attend to his western flanks. Nikephoros may have hoped to embroil them in Balkan warfare, distracting them from attacking Byzantine lands during his own campaigns in Syria and Mesopotamia.