Having thus secured the country he had already overrun, Agricola now prepared for the subjugation of the tribes which lay still farther to the north. The formidable character of this undertaking, even to the experienced Roman general, may be estimated by the cautious and deliberate manner in which he prepared for a great struggle; and in the position in which he then found himself, the conception of such a plan must have required no ordinary power of firm determination. Before him, the more northern regions were protected by a great natural barrier formed by two important arms of the sea, which in any farther advance he must leave behind him. Between these two estuaries he had drawn a line of forts as the formal boundary, for the time, of the province. Beyond them, at the distance of not many miles, were the forts he had placed the year before the last, in which a few of the troops maintained themselves in the precarious possession of a district he acknowledged to be still hostile. On one side the rough line of the Fifeshire coast stretched on the north side of Bodotria, or the Firth of Forth, into the German Ocean. On the other a mountainous region was seen tending towards the Caledonian or Western Ocean; and the northern horizon presented to his view the great range of the so-called Grampians, extending from the vicinity of the Roman stations in one formidable array of mountains towards the north-east as far as the eye could reach. Of the extent of the country beyond them; of the numbers and warlike character of the tribes its recesses concealed; of whether the island still stretched far to the north, or whether he was at no great distance from its northern promontories; of whether its breadth was confined to what he had already experienced, or whether unknown regions, peopled by tribes more warlike than those he had already encountered, stretched far into the Eastern and Western Seas, he as yet knew nothing. [Sidenote: A.D. 82. Fifth summer; visits Argyll and Kintyre.] His first object, therefore, was to form some estimate of the real character of the undertaking before him. With this view, and in order to ascertain the character of the western side of the country before him, he in the fifth summer crossed the Firth of Clyde with a small body of troops in one vessel, and penetrated through the hostile districts of Cowall and Kintyre till he saw the Western Ocean, with the coast running due north, presenting in the interior one mass of inaccessible mountains, the five islands of the Hebudes, and the blue shores of Ireland dimly rising above the western horizon.[49] The character of the country on the west being thus ascertained, he determined to make his attack by forcing his way through the country on the east, and, fearing a combination of the more northern tribes, he combined the fleet with the army in his operations. [Sidenote: A.D. 83-86. Three years’ war north of the Forth.]