including a space varying from five acres and a half to three-quarters of an acre. Each was fortified with a wall and trench of its own. Commonly the Great Wall serves as the north wall of the camp; but sometimes the camp has a north wall of its own. These must have been built before the Great Wall, it may be supposed to shelter the troops and workmen who were engaged in the work. Three stand at some distance to the south. These may have been forts built by Agricola. Each had four gates, streets crossing each other at right angles, after the fashion of Roman camps, and, it would seem, suburbs for the camp followers. No traces of ornamental building, like the tesselated pavements to be seen at Silchester camp, are to be discovered.

b. Mile-castles (castella) were built at average intervals of a Roman mile along the wall. Sometimes they occur more frequently, when a river or a mountain pass is traversed, a castle being commonly placed to guard the defile. These also are four-cornered, measuring fifty feet, or an average, from north to south, and sixty from east to west. These were part of the wall, being of the same masonry, and having it for their northern defence. They had gates in the centre of their northern and southern sides.

c. Between each mile-castle, four Turrets or WatchTowers were built, standing therefore about three hundred feet apart. These may be called sentryboxes. Very little is now left of them, but enough to show that they were very strongly built.

4. The Rampart (Vallum). This fortification con

A Roman mile measured 1,618 yards.

MILITARY ROADS.

73 sists of a trench and three carthern walls. One of these walls stands between the Great Wall and the trench; a second is close upon the southern edge of the trench; the third is as far from it to the south as the first is to the north. The first and third are larger than the second. Their original dimensions cannot be recovered; but, as they still stand six or seven feet high, they were doubtless considerable. A good deal of stone has been used in their construction. The trench seem to have been somewhat smaller than that which was drawn on the north side of the Great Wall. The Vallum is not always close to the Wall. It follows an easier line of country, whereas, as has been said, the wall takes in by choice the most difficult and steepest spots. It does not reach along the whole length of the Wall, but is about three miles short of it at either end.

5. The Roads. Of these there were two.

a. A military way ran along the whole length of the Wall, between it and the Rampart. It was twenty feet wide on an average, and was constructed of stone. It did not always keep close to the wall, but took the shortest route from one camp to another. It was intended, of course, for the rapid and easy transport of troops and stores from one point of the Wall to another, according as they might be needed.

b. A road ran to the south of both Wall and Vallum, and afforded additional accommodation, available when hostilities were not actually going on.

This gigantic work, Wall, Camps, Rampart, and Roads (reckoning only the inner way) constituted one great camp, which might be used against enemies on

either side. For it is not constructed as if the country to the south were permanently friendly. There are no outlets in the Vallum southward, except by the regular gates of the Camps. It must have required at least ten thousand men to garrison it, and, doubtless, could have accommodated, on an emergency, many more.

A second line of defence was constructed by Antoninus Pius, Hadrian's successor. This ran between the Firth of Forth and the Firth of Clyde, and joined together the line of forts built about sixty years before by Agricola. It consisted of a trench, which was forty feet wide and twenty deep, and a rampart, constructed close to the southern edge of the trench, which was twenty feet high and twenty-four feet thick. Other forts were built, so that the intervals between them did not exceed two miles in length, and it was arranged that each should be in sight of its next neighbour. On the southern side of the rampart was a platform for the soldiers, and behind this again ran a military way, twenty feet wide. Some remains of this work are still to be seen. They are known by the name of "Graham's Dyke." The Vallum Antonini, as it is called, was built by Lollius Urbicus between 140 and 145. Urbicus commanded the forces in Britain for twenty years, and pushed the Roman conquests in Northern Britain as far as the Moray Firth. Of the events of the next fifty years we know very little, though we hear of an inroad of the northern tribes, who broke through the rampart of the Upper Isthmus, and were with diffi

That between the Forth and the Clyde.

culty repelled by the General Ulpius Marcellus. This was in the year 184, under the reign of Commodus, the vicious successor of the philosophic Aurelius.

The history of Clodius Albinus, the successor of Marcellus in the command of the British armies, shows the growing importance of Britain among the provinces of the Empire. It was to Rome, what India has been to itself in recent times, the " nursery of captains." No legions had more active employment, no generals had better opportunities of distinguishing themselves, and winning the confidence of their troops. Albinus became so important a person that the Emperor Commodus offered him the title of Cæsar. The honour was declined, and Albinus soon after lost the favour of Commodus by denouncing him as a tyrant. He was superseded in his command, but was strong enough to keep it in spite of the Emperor. Septimius Severus, who came to the throne in 193, again offered him the title of Cæsar. This time it was accepted. But Severus only meant to deceive a rival with whom he did not feel himself at the moment strong enough to contend. His first idea was to get rid of him by assassination, for he sent very kindly letters by the hand of messengers who had secret instructions to demand a private audience of the general and to stab him to the heart. The plot failed, but Albinus saw that he must fight for his life. He crossed over to the mainland, taking with him a part of his army, and encountered Severus near Lugdunum (Leyden). In the battle that followed the

This would mean a rank which may be described as "ViceEmperor," and it would imply the right of succession to the throne.