[Sidenote: A.D. 80. Third summer; ravages to the Tay.] The third year introduced Agricola to regions hitherto untrodden by Roman foot. He penetrated with his army through the hilly region which separates the waters pouring their floods into the Solway from those which flow towards the Clyde. He entered a country occupied by ‘new nations,’[46] and ravaged their territories as far as the estuary of the ‘Tavaus’ or Tay. His course appears, so far as we can judge by the remains of the Roman camps, to have been from Annandale to the strath of the river Clyde, through Lanarkshire and Stirlingshire, whence he passed into the vale of Stratherne by the great entrance into the northern districts during the early period of Scottish history—the ford of the Forth at Stirling, and the pass through the range of the Ochills formed by the glen of the river Allan, and reached as far as where the river Tay flows into the estuary of the same name.[47] The country thus rapidly acquired was secured by forts, which, says the historian, were so admirably placed, that none were either taken or surrendered; and these we can no doubt still recognise in the remains of those strong Roman fortified posts which we find placed opposite the entrance of the principal passes in the Grampians—the stationary camps of Bochastle at the Pass of Leny, Dealgan Ross at Comrie, Fendoch at the pass of the Almond, the camp at the junction of the Almond and the Tay, and the fort at Ardargie. These obviously surround the very territory which Agricola had just overrun, and are well calculated to protect it against the invasions of the natives from the recesses of the mountains, into which the Roman arms could not follow them; while the great camp at Ardoch marks the position of the entire Roman army. In consequence of these posts being thus maintained, the Roman troops retained possession of the newly-acquired territory during the winter. [Sidenote: A.D. 81. Fourth summer; fortifies the isthmus between Forth and Clyde.] Agricola, with his usual policy, took measures still further to secure the country he had already gained before he attempted to push his conquests farther; and the position of the Firths of Forth and Clyde, and the comparatively narrow neck of land between these, presented itself to him as so remarkable a natural boundary, that he fixed upon it as the frontier of the future province. The fourth summer was therefore spent in securing this barrier, which he fortified by a chain of posts from the eastern to the western firth.[48] From the shores of the Forth in the neighbourhood of Borrowstounness to Old Kilpatrick on the Clyde, these forts extended westward at intervals of from two to three miles. In front of them stretches what must have been a morass, and on the heights on the opposite side of the valley are a similar range of native hill-forts.