The enemy, having learnt this disposition of the Roman army, resolved to make a night attack upon its weakest division, and appear to have crossed the river, passed the main body in the night, and suddenly fallen upon the ninth legion. The camp at Lintrose has only one gate on the side towards the larger camp at Cupar-Angus. On the opposite side the rampart is broken in the centre by the remains of a morass. The enemy forced their way through the gate, having taken the Romans by surprise, and an engagement commenced in the very camp itself, when Agricola, having received information of their march, followed closely upon their track with the swiftest of the horse and foot from the main division of the army, overtook them about daybreak, and attacked them in the rear. The natives were now between two enemies, and a furious engagement ensued, till they forced their way through the morass, and took refuge in the woods and marshes.[50] The Romans were now as much elated by this successful contact with the enemy as they had before been alarmed, and demanded to be led into the heart of Caledonia. The natives attributed their defeat to the fortunate chance for the Romans of their being hemmed in between two forces, and prepared for a more vigorous struggle the following year. A general confederacy of the northern tribes was formed, and ratified by solemn assemblies and sacrifices, and the two contending parties separated for the winter, prepared for a vital contest when they resumed operations next year. This campaign had lasted for two seasons, and Agricola probably returned to the camp at Grassy Walls for winter quarters.[51] The third season was destined to determine whether the Romans were to obtain possession of the whole island, or whether the physical difficulties of the mountain regions of the north, and the superior bravery of its inhabitants, were at last to oppose an obstacle to the further advance of the Roman dominion. Agricola commenced the operations of this year by sending his fleet, as soon as summer arrived, down the coast to the north, to operate a diversion by creating alarm and ravaging the country within reach of the ships. He then marched forward with his army nearly on the track of the preceding year, and crossed the river Isla till he reached a hill, called by Tacitus ‘Mons Granpius,’[52] on which the assembled forces of the natives were already encamped under the command of a native chief, Calgacus, whose name is indelibly associated with the great battle which followed. [Sidenote: A.D. 86. Battle of ‘Mons Granpius.’]