In his absence, Pereyaslavets had been recovered by Boris II; the Bulgarian defenders put up a determined fight, but Sviatoslav stormed the city. Thereafter Boris and Roman capitulated, and the Rus' rapidly established control over eastern and northern Bulgaria, placing garrisons in Dorostolon and the Bulgarian capital of Preslav. There Boris continued to reside and exercise nominal authority as Sviatoslav's vassal. In reality he was little more than a figurehead, retained in order to lessen Bulgarian resentment at and reaction to the Rus' presence. Sviatoslav appears to have been successful in enlisting Bulgarian support. Bulgarian soldiers joined his army in considerable numbers, tempted partly by the prospects of booty, but also enticed by Sviatoslav's anti-Byzantine designs and probably mollified by a shared Slavic heritage. The Rus' ruler himself was careful not to alienate his new subjects: he forbade his army from looting the countryside or plundering cities that surrendered peacefully. Thus Nikephoros' scheme had backfired: Instead of a weak Bulgaria, a new and warlike nation had been established at the Empire's northern border, and Sviatoslav showed every intention of continuing his advance south into Byzantium. The emperor tried to get the Bulgarians to resume the war against the Rus', but his proposals were not heeded. Then, on 11 December 969, Nikephoros was murdered in a palace coup and succeeded by John I Tzimiskes (r. 969–976), to whom fell the task of dealing with the situation in the Balkans. The new emperor sent envoys to Sviatoslav, proposing negotiations. The Rus' ruler demanded a huge sum before he would withdraw, insisting that otherwise the Empire should abandon its European territories to him and withdraw to Asia Minor. For the time being, Tzimiskes was preoccupied with consolidating his position and countering the unrest of the powerful Phokas clan and its adherents in Asia Minor. He therefore entrusted the war in the Balkans to his brother-in-law, the Domestic of the Schools Bardas Skleros, and to the eunuch stratopedarch Peter. In early 970, a Rus' army, with large contingents of Bulgarians, Pechenegs, and Magyars, crossed the Balkan Mountains and headed south. The Rus' stormed the city of Philippopolis (now Plovdiv), and, according to Leo the Deacon, impaled 20,000 of its surviving inhabitants.