Vidin emerged at the place of an old Celtic settlement known as Dunonia. The settlement evolved into an Roman fortified town called Bononia. The town grew into one of the important centers of the province of Upper Moesia, encompassing the territory of modern northwestern Bulgaria and eastern Serbia. Roman rule lasted until 46 AD. At the decline of the empire, the Goths, Huns, Bulgars, and Avars invaded. The Bulgars, who crossed the Danube from the north in 679, took control of the region. In 865, the area adopted Orthodox Christianity. The Bulgars twice conquered most of the Balkan peninsula between 893 and 1280.