During the reign of Emperor Peter I, Bulgaria prospered in a long-lasting peace with Byzantium. This was secured by the marriage of Peter with the Byzantine princess Maria Lakapina, granddaughter of Byzantine Emperor Romanos I Lekapenos. However, after Maria's death in 963, the truce had been shaken and it was at this time or later that Peter I sent his sons Boris and Roman to Constantinople as honorary hostages, to honor the new terms of the peace treaty. During these years the Byzantines and Bulgarians had entangled themselves in a war with Kievan Rus' Prince Sviatoslav, who invaded Bulgaria several times. After a defeat from Sviatoslav, Peter I suffered a stroke and abdicated his throne in 969 (he died the next year). Boris was allowed back to Bulgaria to take his father's throne, restore order and oppose Sviatoslav, but had little success. This was allegedly used by Nicholas and his sons, who were contemplating a revolt in 969.