To gain Oyarzun, a small town eight miles beyond the Bidassoa and close to Passages, was Soult’s object, and a royal road led directly to it by a broad valley between the Peña de Haya and Jaizquibel mountains; but the Peña de Haya, called also the four-crowned mountain, filled all the space between Vera, Lesaca, Irun and Oyarzun, and its staring head, bound with a rocky diadem, was impassable: from the bridges of Vera and Lesaca, however, roads, one of them not absolutely impracticable for guns, passed over its enormous flanks to Irun on one side, to Oyarzun on the other, falling into the royal road at both places. Soult therefore proposed to drive the light division from Santa Barbara, and use the bridges of Lesaca and Vera to force a passage over the Peña de Haya on his own right of its summit, pushing the heads of columns towards Oyarzun and the Upper Urumea, while Reille and Villatte, passing the Bidassoa at Biriatu, forced their way by the royal road.
Soon he changed this plan, and with great caution and subtilty brought his left from St. Jean Pied de Port to his right, masking the movement by his cavalry, and thus formed two columns of attack on the Lower Bidassoa. One under Clausel, of twenty thousand men with twenty pieces of artillery, was concentrated in the woods behind the Commissari and Bayonette mountains above Vera. The other under Reille, eighteen thousand strong, was placed on the Lower Bidassoa, having Foy’s division and some light cavalry in the rear ready to augment it to twenty-five thousand. Thirty-six pieces of artillery and two bridge equipages were disposed near Urogne, on the royal road, all being secreted behind the lower ridge of the mountains near Biriatu.
Soult’s first design was to attack at daybreak on the 30th, but his preparations being incomplete he deferred it until the 31st, taking rigorous precautions to prevent intelligence passing over to the allies; Wellington’s emissaries had, however, told him in the night of the 29th that the French were in movement, and the augmentation of troops in front of Irun was observed in the morning of the 30th. In the evening the bridge equipage and the artillery were discovered on the royal road, and thus warned he prepared for battle with little anxiety; for a fresh brigade of English foot-guards, most of the marauders and men wounded at Vittoria, and three regiments from England, forming a new brigade under Lord Aylmer, had recently joined.
His extreme left was on the Jaizquibel, a narrow mountain-ridge seventeen hundred feet high, running along the coast and abutting at one end on the Passages harbour, at the other on the navigable mouth of the Bidassoa. Offering no mark for attack, it was only guarded by some Spaniards; but the small fort of Figueras, commanding the entrance of the river at its foot, was garrisoned by seamen from the naval squadron, and Fuenterabia, a walled place, also at its base, was occupied.
The low ground between Fuenterabia and Irun was defended by large field redoubts, connecting the Jaizquibel with some heights covering the royal road to Oyarzun.
On the right of Irun, between Biriatu and the burned bridge of Behobia, a sudden bend in the river presented the convex to the French, who thus commanded the fords; but beyond those fords was a stiff and lofty ridge, called San Marcial, terminating one of the great flanks of the Peña de Haya. The water flowed round the left of this ridge, confining the road from the Behobia bridge to Irun, one mile, to the narrow space between the channel and the foot of the height; Irun itself, defended by a field-work, blocked this way; and hence the French, after passing the river, had to win San Marcial before they could use the great road; but six thousand Spaniards occupied that strong ridge, which was strengthened by abbattis and temporary field-works.
Behind Irun the first British division was posted under General Howard, and Lord Aylmer’s brigade supported the left of the Spaniards.
San Marcial, receding from the river on the right, was exposed to an enemy passing above Biriatu; but Longa’s Spaniards, drawn off from those slopes of the Peña de Haya descending towards Vera, were posted on those descending towards Biriatu, where they supported the right of the Spaniards on San Marcial.
Eighteen thousand fighting men were thus in position, and as the fourth division was still disposable, a Portuguese brigade was detached from it to replace Longa near Vera, and cover the roads from that place over the flanks of the Peña de Haya. The British brigades of that division were stationed up the mountain, near the foundry of San Antonio, commanding the intersection of the roads coming from Vera and Lesaca, and furnishing a reserve to the Portuguese brigade, to Longa, and to San Marcial—tying all together. The Portuguese brigade being however too weak to guard the enormous slopes near Vera, Inglis’s brigade was drawn from Echallar to reinforce it; yet the flanks of the Peña de Haya were so rough and vast the troops seemed sprinkled rather than posted.
In the night of the 30th Soult placed his guns, and gave his orders. Reille was to storm San Marcial, to leave a strong reserve there to meet troops coming from Vera or descending the Peña de Haya, and with the rest of his force drive the allies from ridge to ridge, until he gained the slope of the mountain which descends upon Oyarzun. When the royal road was thus opened, Foy’s infantry, with the cavalry and artillery in one column, were to cross by bridges to be laid during the fight.