Throughout the third century the Roman Empire, decaying socially and disintegrating morally, faced the barbarians. The emperors of this period were fighting military autocrats, and the capital of the empire shifted with the necessities of their military policy. Now the imperial headquarters would be at Milan in north Italy, now in what is now Serbia at Sirmium or Nish, now in Nicomedia in Asia Minor. Rome halfway down Italy was too far from the centre of interest to be a convenient imperial seat. It was a declining city. Over most of the empire peace still prevailed and men went about without arms. The armies continued to be the sole repositories of power; the emperors, dependent on their legions, became more and more autocratic to the rest of the empire and their state more and more like that of the Persian and other oriental monarchs. Diocletian assumed a royal diadem and oriental robes. All along the imperial frontier, which ran roughly along the Rhine and Danube, enemies were now pressing. The Franks and other German tribes had come up to the Rhine. In north Hungary were the Vandals; in what was once Dacia and is now Roumania, the Visigoths or West Goths. Behind these in south Russia were the East Goths or Ostrogoths, and beyond these again in the Volga region the Alans. But now Mongolian peoples were forcing their way towards Europe. The Huns were already exacting tribute from the Alans and Ostrogoths and pushing them to the west. In Asia the Roman frontiers were crumpling back under the push of a renascent Persia. This new Persia, the Persia of the Sassenid kings, was to be a vigorous and on the whole a successful rival of the Roman Empire in Asia for the next three centuries. A glance at the map of Europe will show the reader the peculiar weakness of the empire. The river Danube comes down to within a couple of hundred miles of the Adriatic Sea in the region of what is now Bosnia and Serbia. It makes a square re-entrant angle there. The Romans never kept their sea communications in good order, and this two hundred mile strip of land was their line of communication between the western Latin-speaking part of the empire and the eastern Greek-speaking portion. Against this square angle of the Danube the barbarian pressure was greatest. When they broke through there it was inevitable that the empire should fall into two parts. Map: The Empire and the Barbarians