Sviatoslav readily launched a campaign with a vast force of 60,000 troops, routed the Bulgarians on the Danube, and defeated them in a battle near Silistra, seizing some 80 Bulgarian fortresses in 968. Stunned by the success of his ally and suspicious of his actual intentions, Emperor Nikephoros II hastened to make peace with Bulgaria and arranged the marriage of his wards, the underage emperors Basil II and Constantine VIII, to two Bulgarian princesses. Two of Peter's sons were sent to Constantinople as both negotiators and honorary hostages. In the meantime Peter managed to secure the retreat of the Rus forces by inciting Bulgaria's traditional allies, the Pechenegs, to attack Kiev itself.