The Last Days of the Legion A.D. 235–450

      Book I, Chapter I

                  BETWEEN the middle of the third and the middle of the fifth century lies a period of transition in military history, an epoch of transformations as strange and as complete as those contemporary changes which turned into a new channel the course of political history and of civilisation in Europe. In war, as in all else, the institutions of the ancient world are seen to pass away, and a new order of things develops itself.

                  The most characteristic symptom of the tendencies of this period is the gradual disappearance of the Roman legion, that time-honoured organisation whose name is so intimately bound up with the story of Roman greatness. In A.D. 250 it was still the heavy-armed infantry of the empire which formed the core of battle, and was the hope and stay of the general. By A.D. 450 the cavalry was all in all, the foot-soldiery had fallen into disrepute, and the very name of legion was almost forgotten. It represented a form of military efficiency which had now completely vanished. That wonderful combination of strength and flexibility, so solid and yet so agile and easy to handle, had ceased to correspond to the needs of the time. The day of the sword and pilum had given place to that of the lance and bow. The typical Roman soldier was no longer the iron legionary, who, with shield fitted close to his left shoulder and sword-hilt sunk low, cut his way through the thickest hedge of pikes, turned back the onset of the mailed horsemen of the East, and stood unmoved before the wildest rush of Celt or German. The old military organisation of Augustus and Trajan began to fall to pieces in the third century; in the fourth it was so weakened and transformed as to be hardly recognisable; by the end of the fifth it had disappeared.

                  The change in the character of the Roman army which ultimately substituted cavalry and light infantry for the solid strength of the ancient legion was mainly caused by the exigencies of border-warfare. From the time of Hadrian to that of Severus, the system of frontier-defence which the Roman Government adopted was to fix the limit of the empire at a great natural boundary, such as the Rhine, Danube, or Euphrates, and to place behind the boundary at suitable points large permanent camps, in which one or more legions were quartered. These garrisons were placed many scores or even hundreds of miles apart, and the long intervals between them were only filled by minor posts occupied by small bodies of auxiliary troops. Where natural obstacles, such as rivers or mountain-chains, were wanting, the frontier was not unfrequently marked out by long lines of entrenchments, like our own Northumbrian Wall, or the similar structure which stretches across South Germany. The stations were connected with each other by good military roads, and the alarm could be passed from one to another at the shortest notice by a system of beacons and mounted messengers. If the barbarous enemy across the frontier, German, Sarmatian, or Parthian, essayed a raid on Roman territory, he must first cross the obstacles and then cope with the garrisons of the local posts. These would be able to beat back any small plundering parties; but if they found the invaders too strong, they could at least endeavour to harass them, and to restrict the area of their ravages, till the nearest legion could march up from its great permanent camp.

                  This system worked well for more than a hundred years. But it had its weak points; there was a great want of a central reserve, in case the legions of any frontier should be unable to hold their ground against an attack of unusual strength. For the middle provinces of the empire were kept entirely denuded of troops, and new legions could not be improvised in a hurry from the unwarlike subjects of the empire, as they had once been from the citizens of the early republic. Hence it came to pass that a disaster on one point of the border had to be repaired by drawing troops from another. This rather dangerous device could only be employed so long as the enemies of Rome were so obliging as to present themselves one by one, and to refrain from simultaneous onslaughts on far distant tracts of frontier. For more than two centuries the empire was fortunate enough to escape this contingency; its military system was never tried by the crucial test of an attack all along the line; in the times of stress Germany could lend troops to Britain, or Moesia reinforce the legions of Syria. Disasters were suffered from time to time which threw a province for a moment into hostile hands, but because they came singly they could always be repaired. The rebellion of Civilis shook the Roman hold on the Rhine frontier for a space; the defeat of Domitian’s generals Sabinus and Fuscus let the Dacians into the interior of the Danube provinces; Marcus Aurelius once saw the Quadi at the gates of Aquileia. But reinforcements were brought up from frontiers where no war was in progress, and the incoming flood of invasion was at length stemmed.

                  In the third century there was a complete change in the face of affairs: the system of defence broke down, and the empire well-nigh collapsed under the stress. From the day of the murder of Alexander Severus (A.D. 235) to the moment at which Diocletian put down the last surviving rebel Caesar in the remotest comer of the West (297) the empire was subjected without a moment’s respite to the double scourge of civil war and foreign invasion. In the space of sixty years no less than sixteen emperors and more than thirty would-be emperors fell by sword or dagger. While the arms of the legions were turned against each other, the opportunity of the enemies of the empire had arrived. All its frontiers simultaneously were beset by the outer barbarians, and the fabric reeled before the shock. For Rome’s neighbours were growing more powerful just when Rome herself was weak and divided. The new and vigorous Persian kingdom had just replaced the decrepit Parthian power in the East (A.D. 226). The Germans were already commencing to form the confederacies which made their scattered tribes for the first time really formidable. The names of the Franks, Alamanni and Goths begin to appear along the Rhine and Danube.

                  So long as the frontier defence of the legions held firm, the empire presented to its foes a hard shell and a soft kernel. The border was strongly held and difficult to pierce, but the rich provinciae inermes within were defenceless and ripe for plunder, if only the shell could be pierced. When the legions were withdrawn from the frontier to take part in civil war, and marched off time after time to enthrone some new usurper upon the Palatine, it was impossible to keep back any longer the pressure from without. The period 235–297 opens with a heavy and long-continued onslaught of the Quadi Carpi and Goths on the Middle and Lower Danube (236). It was beaten back by Maximinus I and Philip for a few years; but in 249, while a vigorous civil war was distracting the Illyrian regions, the line of resistance was at last broken through. The Goths crossed the Danube and Balkans, overran Moesia and Thrace, and scattered the Imperial troops before them. The Emperor Decius, having put down his rivals, hastened to meet them; but he, his son, and his whole army were cut to pieces in the disastrous battle of Forum Trebonii in the summer of 251. No Roman emperor had ever been slain before in battle with the barbarians; no Roman host of such strength had suffered defeat since the day of Cannae. It seemed for a moment as if the empire was fated to be cut in twain, or even as if some earlier Alaric were about to present himself before the gates of Rome.

                  For the next twenty years the Goths ranged almost unresisted over the middle provinces of the empire. The troops that should have been called in to resist them were occupied in civil wars in Italy, or were employed in defending other menaced frontiers. For, while the Gothic war was at its height, the Persian king Sapor overran Mesopotamia, defeated and took captive the Emperor Valerian, stormed Antioch, and ravaged Syria and Asia Minor (258–259). Favoured by these distractions, the Goths were able to carry all before them in the central provinces of the empire. Not only did they harry the whole Balkan peninsula as far as Athens and Dyrrachium, but daring bands of plunderers crossed the Hellespont and sacked Chalcedon, Alexandria Troas, Ephesus, and even the distant Trebizond. With a little more guidance and a single leader at their head, they might have made an end of the empire, for usurpers were rising in every province. Civil war had become endemic among the Romans; the Germans of the Rhine frontier were battering at the defences of Gaul and Rhaetia; and the indolent and frivolous Gallienus, who still maintained his precarious seat on the Palatine, bade fair to be the Sardanapalus of Rome, and to see city and empire go down together in one universal conflagration of civil strife and foreign war. In the years 260–268 all seemed lost. But deliverers arose – the tough Illyrians, Claudius, Aurelian, and Probus, reconquered the West from rebel Caesars, cleared the Germans out of the Balkan peninsula, and won back the East from the Persians and the Palmyrenes. Soon after came Diocletian, the reorganiser and restorer, and with the reconquest of...