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and of different extent and strength. After the successful campaign of Tacitus into Caledonia, that wary and judicious general, in the year of our Lord 8 1 , drew a line of communicating forts between Glota and Bodotria, Forth and Clyde; both to secure his own conquests, and to shut up the Cale- donians (as he expresses it) in another island; Summotis velut in aliam insulam hostibus. For a few years this fortification answered the intended pur- pose; but the Roman government becoming more lax, and the Caledonians bolder and more vigilant, they at length pushed their arms beyond the forts ; which led Adrian, on his arrival in England in the year 121, to raise a new boundary. This he ef- fected by digging a ditch, and throwing up ^vallum constructed of earth and stones, eighty miles in length, beginning at Brough, on the Solway sands, and ending at Wall's-End. Lollius Urbicus, the lieutenant of Antoninus, repossessing himself of the a turf wall on the line of that great commander's forts. Seventy years afterwards, Sevcrus, wisely gh ing up a territory of little value, to be retained only with difficulty, built the immense vallum on v. Iiich v e now were, of uncertain height, but from
- t 1 remains proved to be eight feet in thickness;
strengthened with numerous towers, about a mile
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