These were consuls in A.D. 158; consequently, we have undeniable authority to assert, that Antoninus Pius repaired Hadrian’s Vallum (or, at least, the stations _per lineam Valli_), as well as built one between the Scottish Firths. This stone is certainly most valuable, as it clearly proves, that though Antoninus extended the boundary so far north, he could not, or durst not, trust the Mæatæ, but thought himself obliged to keep up the southern pretenturæ, lest they should, on any disturbance, join the Caledonians. Such prudence is characteristic of good generalship. Napoleon never made an important move without first resolving what to do in case of failure. Assuredly Hadrian did not act in a manner unbecoming a Roman, when, at the same time that he shewed a stony front to the Caledonians, he placed an earthen rampart between himself and the doubtful fidelity of his southern subjects. [Sidenote: THE BARRIERS IN RELATION TO THE RIVERS.] The position of the Barriers of the Lower and of the Upper Isthmus, and of the Devil’s Wall, in relation to the rivers in their vicinity, requires some remark. The Tyne in the eastern, and the Irthing and the Eden in the western part of the island, are uniformly to the south of the English Wall. A similar remark applies to the Devil’s Wall, in Germany, which is drawn along the northern shore of the Danube, the side exposed to the enemy. The Clyde, and its feeders, are to the south of the Antonine Wall. Why did the Romans not avail themselves of the natural trenches of these river-basins? The valley of the Tyne is peculiarly broad and deep. A chain of camps on its southern bank, where the mediæval castles afterwards stood, would alone, we might suppose, have bid defiance to the passage of any foe. A similarity of practice in these cases favours the belief that important objects were to be accomplished by it. What are they?— By erecting a chain of posts on the high grounds to the north of the rivers, a better observation of the movements of the enemy was obtained than would otherwise have been practicable. In the days of Roman occupation, large tracts of country, the banks of rivers especially, would be covered with forests. The conquerors, unless they had secured the enemy’s side of the river-basins, would have been perpetually subject to unexpected attacks. They could not be so easily taken by surprise on the high grounds of the northern slopes. [Sidenote: IMPORTANCE OF RIVER BASINS.]