Sviatoslav retreated to Dorostolon, which the Byzantine armies besieged for sixty-five days. Cut off and surrounded, Sviatoslav came to terms with John and agreed to abandon the Balkans, renounce his claims to the southern Crimea, and return west of the Dnieper River. In return, the Byzantine emperor supplied the Rus' with food and safe passage home. Sviatoslav and his men set sail and landed on Berezan Island at the mouth of the Dnieper, where they made camp for the winter. Several months later, according to the Primary Chronicle, their camp was devastated by famine, so that even a horse's head could not be bought for less than a half-grivna. While Sviatoslav's campaign brought no tangible results for the Rus', it weakened the Bulgarian state and left it vulnerable to the attacks of Basil the Bulgar-Slayer four decades later.