During this march Severus is said to have fought no battle, his system of opening up the country and rendering it passable for his troops, insuring him its possession as he slowly advanced; but the natives appear to have carried on a kind of guerilla warfare against the parties engaged in these works, assailing them at every advantage, and enticing them into the woods and defiles by every stratagem, so that, although Severus’s progress was sure, his loss is said to have been very great. This circumstance on his part, and the effect upon the natives of his success in penetrating to a point which no Roman invader had hitherto reached, or even attempted, led eventually to a peace, the principal condition of which was that the native tribes should yield up a considerable part of their territory to be garrisoned by Roman troops. The part ceded could hardly have been any other district than that extending from the northern wall to the Tay, a district which Agricola had likewise held to a limited extent in advance of the frontier he designed for the province, and this is confirmed by the existence of a temporary camp and a strong station at Fortingall, not far from where the river Tay issues from the lake of the same name. It appears to have been an outpost beyond the Tay, and there is no known circumstance connected with the Roman occupation of Britain to which its existence can be attributed, with any probability or with any support from authority, save this cession of territory to Severus. There is a similar camp and station at Fendoch on the banks of the Almond, where it emerges from the Grampians, and a corresponding camp and station at Ardoch, which can be distinguished from Agricola’s camp there. A part of the inhabitants of this district, too, made their appearance about this time in the Roman army, and two inscriptions found at Nieder Biebr on the Rhine, one of which is dated in 239, show that there were stationed there troops composed of the Horesti, and of the people who possessed Victoria as their chief seat, from which it would appear that Severus had enrolled bodies of the inhabitants of the ceded district among the Roman auxiliaries.[80] These are all marks of Severus’s occupation of this district, and, as there are traces of Roman works on the Spey at Pitmain, on the line between the Moray Firth and Fortingall, it would appear that Severus with a part of the army had returned through the heart of the Highlands. [Sidenote: Severus’s wall.] Having thus concluded a peace with the Caledonii and Mæatæ, and compelled them to yield up to him a part of their territory north of the wall to be occupied by his troops in advance of the frontier, Severus proceeded to reconstruct the wall between the Forth and the Clyde, as the actual boundary of the province. He appears to have added the large fosse or ditch, to have placed additional posts along the wall, and to have repaired and strengthened the structure itself.[81]