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 {11} 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. [Sidenote: 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.