 From there, Asparukh's cavalry in alliance with local Slavs annually attacked the Byzantine territories in the south.In 680, the Byzantine Emperor Constantine IV led a large army to fight the Bulgars but was defeated in the battle of Ongal and the Byzantines were forced to acknowledge the formation of a new country, the First Bulgarian Empire.The northern border of the country followed the southern slopes of the Carpathian mountains from the Iron Gates and reached the Dneper river or possibly just the Dniester river to the east.