Ere twenty years had elapsed since this description of the tribes of the barbarian portion of Britain was written, the frontier of the Roman province had been advanced from the wall between the Solway and the Tyne to the isthmus between the Forth and Clyde, the boundary destined for it by the sagacity of Agricola. Early in the reign of Antoninus, who succeeded Hadrian in the empire in the year 138, the independent portion of the nation of the Brigantes had broken the bounds set to them by the wall of Hadrian, and overrun the territories of one of the provincial tribes, and thus drew upon themselves the vengeance of the Roman Emperor. Lollius Urbicus was sent into Britain in the second year of his reign, towards the end of the year 139, subdued the hostile tribes, and constructed an earthen rampart between the Firths of Forth and Clyde, thus advancing the frontier of the Roman province to the isthmus between these firths, and again adding the intermediate territory to the Roman possessions in the island. This wall between the Forth and Clyde remained from this time, till the Romans left the island, the proper boundary of the province during the entire period of their occupation of Britain.[70] The isthmus between the Forth and Clyde presents towards the west the appearance of a great valley, having the Campsie and Kilsyth hills on the north, and on the south a series of lesser rising grounds extending in a continuous line from sea to sea; while the hills on the opposite side recede as the valley approaches towards the east, till the view from the southern rising ground extends over the magnificent plain of the Carse of Falkirk, with the upper part of the Firth of Forth stretching along its northern limit. The Roman wall was constructed along the ridge of the southern rising grounds, and the remains of this stupendous work have at all times arrested the attention of even the careless observer. This great work, as it presents itself to the inspection of those who have examined it minutely, consisted of a large rampart of intermingled stone and earth, strengthened by sods of turf, and must have originally measured 20 feet in height, and 24 feet in breadth at the base. It was surmounted by a parapet having a level platform behind it, for the protection of its defenders. In front there extended along its whole course an immense fosse, averaging about 40 feet wide and 20 feet deep. To the southward of the whole was a military way, presenting the usual appearance of a Roman causewayed road. This great barrier extended from Bridgeness, near Carriden, on the Firth of Forth, to Chapelhill, near West Kilpatrick, on the Clyde, a distance of twenty-seven English miles,—having, at intervals of about two miles, small square forts or stations, which, judging from those that remain, amounted in all to nineteen in number, and between them were smaller watch-towers.[71]