The object of the enemy now was to occupy a position behind the Ebro, blocking up the great road by placing a garrison in the castle of Pancorbo, and calling to their assistance the corps from Biscay, Navarre, and Aragon. But Lord Wellington, repeating the manœuvre which had before so perfectly succeeded, had already sent his left column to effect its passage in a quarter from whence they apprehended no danger. The Ebro rises in the mountains of Santillana, its principal source being at the northern extremity of Old Castille, towards the Asturian frontier, near a town which from that cause is called Fontibre. The Sierra de Oca prevents it from trending westward, like the other great rivers of Spain; and at Miranda de Ebro, the point at which the Intruder had instructed the different divisions of his army to make for with all speed, it appears nearly as large a stream as at Tortosa, though in the course of the intervening sixty leagues it receives many and large rivers, one of them the Aragon, of such magnitude, that it is called the husband (_el varou_) of the Ebro. While the remainder of the army were pushing the enemy back ♦PASSAGE OF THE EBRO BY THE ALLIES.♦ upon Burgos, the left column had been detached to effect its passage above Frias by the bridges of S. Martin and Rocamunde: the road thither had been deemed impracticable for carriages, and on that supposed impracticability the enemy relied; but the confidence of the British General was partaken by his army, and well seconded by them in all ways; exertions which nothing but zeal and eager hope could have accomplished were made; and the artillery was lowered down the steep banks of the river where there were none to offer any resistance. The French had calculated not without reason on the line of the Ebro, if they had had foresight or been allowed leisure to occupy it. The road begins to descend the mountains about three miles from the right bank, and for more than half that way winds down a continued defile, which admits only eight or ten men abreast, and being withal tremendously steep, is so paved that horses can scarcely keep their feet there. Another such defile, and of greater length, is to be passed on the opposite side. A few ditches cut across the route, a few trees placed as barricadoes, a rock blown up to block the pass, a hundred or two of men to defend it, and to roll stones from the crags and precipices above, might have stopped any force that attempted the passage. The left column crossed on the 14th, the remainder of the army on the 15th, at the same points and by the Puente de Arenas, and on the following day they moved to the right, in the direction of Vittoria.