The legions, as we have seen already, might be moved hither and thither to any point of the great Empire where their services were needed. While the Empire was being created, and the nations were being subdued, there was frequent occasion for this movement of large bodies of troops; but you must realise that we have now come to a point in the story at which the Empire—especially under the wise Emperor Hadrian—is concerned more with making good the conquests it has already won, than in adding to them. The boundaries, the limits, have been set, as we have just been tracing them—or somewhat like that. The Romans are within the boundaries; the barbarians are without. And wherever the barbarians are there is need of one or other of the legions, acting as a kind of police, to see that no one breaks through the wall.
The result of that is that the legions are not required to move about so much as they were when the Empire was being won. Now that it is won, they are set here and there, like watch dogs, along the boundaries. The positions which they occupy become permanent camps. The legionaries are allowed to marry and to live outside the actual confines of the camp.
The Legions in Britain
I think this then may give us some general idea of the picture that we should carry in our minds of the Roman Empire—which is almost as much as to say, of the world—at this point in the story, about A.D. 200. There are in all twenty-five legions. In Britain itself there were three, one at Chester, one at York, one at Caerleon. Now the number of troops in a legion was commonly, as we have seen, 6,000, but twenty-five of these legions did not nearly represent the total army of the Roman Empire, because to each of the legions was attached at least an equal number of auxiliaries, light-armed troops. Thus the establishment of a legion in any district meant a huge increase of population, a very large castrum or camp, from which we get the names of such places as Man-chester, Dor-chester, and Chester itself—Chester being a modification of the Roman word castrum. Besides the auxiliaries, who were light-armed foot-soldiers, there were a few mounted troops attached to each legion, but the chief of the fighting was supposed to be done by the legionaries, or soldiers of the legions. Just as we saw that among the Greeks the hoplites, the heavy-armed soldiers of the phalanx, were considered to form the strength of the army, so it was with the heavy-armed legionaries of the Romans.
The tradition was still kept up, that the legionaries should be men who had the privileges of free citizens of Rome, while the auxiliaries were taken from a lower class of the people who had not these privileges. But we have seen that this privilege was given to more and more as time went on, so that Roman citizenship ceased to be as valuable as it once was, because it had become more common. Recruits to the legions were taken from the natives of the conquered lands. Moreover, since the legionaries in these settled camps were allowed to marry, their sons were naturally disposed to become soldiers, like their fathers, when they grew up.
Legions independent
The effect of all this was to make the legions very closely attached to the places in which their permanent camps were pitched. The camps became home to them. They no longer looked to Rome as their home; and by degrees they ceased to look to Rome as the centre at which what we should call their Headquarter Staff resided. They became more and more independent of Rome. If an attack came, or was threatened, from the barbarians beyond the limits which they had to guard, they dealt with the threat or the attack. They were not obliged to send back to Rome for their instructions.
Realise then, for it is of much importance in the development of the great story, the increasing independence of the legions in their large camps, when once these camps had been established as permanent settlements. We left the story, at the end of the first volume, at a point where its threads had been gathered together in the great hand of the Roman Empire. This second volume is largely occupied with the disruption and pulling apart of those threads out of that hand; and the reason why the hand was obliged to relax its grasp and so allow the threads to be torn apart again is twofold. One part of the reason is this independence of the "far flung" legions, which became less and less attentive and obedient to orders from the centre at Rome. Another part of the reason is that the barbarians beyond the limits began knocking at the walls harder and harder and finally broke through.
What is so interesting to see in this story is not only the events that happened, but also (and perhaps more interesting still) the explanation why they happened as they did. I have tried to make clear how it was that the armies of the Empire grew to be almost independent of any orders coming from the centre, and how that independence partly explained the break-up of the Empire.
I must now try to make clear to you why it was that the barbarians knocked as they did at the walls and finally broke through them and so completed the disruption of the power of Rome.