The original duchy was bound by the Carnic Alps and Julian Alps to the north and northeast and was hardly accessible from those directions. It was bound by the Byzantine Exarchate of Ravenna to the south, where it did not have a coastline until later, and by a plain that led to the Pannonian Basin in the east, a perfect access point for invaders, such as the Avars and later the Magyars. Its western border was originally undefined, until further conquests had established the Lombard duchy of Ceneda, which lay beyond the Tagliamento river, between the Livenza and the Piave Rivers. From the beginning, then, the Duchy of Friuli had a military role which it retained throughout the whole period of the Lombard kingdom and meant that it always played an important role in Italian politics, such that several of its dukes achieved the rank of king.