On Soult’s side each lieutenant-general had a special position to defend. The left of D’Erlon’s first line, resting on the fortified rocks of Mondarain, could not be turned; his right was on the Nivelle, and the whole, strongly intrenched, was occupied by one of Abbé’s and one of D’Armagnac’s brigades. The second line, on a broad ridge several miles behind, was occupied by the remaining brigades of those divisions, and its left did not extend beyond the centre of the first line; but the right reached to the bridge of Amotz, where the Nivelle, flowing in a slanting direction, gave greater space. Three great redoubts were in a row on this ridge, and a fourth had been commenced close to the bridge.
On the right of D’Erlon’s second line, that is to say beyond the bridge of Amotz, Clausel’s position extended to Ascain, along a strong range of heights fortified with many redoubts, trenches, and abbatis; and as the Nivelle, after passing Amotz, swept in a curve completely round this range to Ascain, both flanks rested alike upon that river,—the bridges of Amotz and Ascain being close on the right and left, and a retreat open by the bridges of San Pé and Harastaguia in rear of the centre. Two of Clausel’s divisions, reinforced by one of D’Erlon’s under General Maransin, were there posted. In front of the left were the redoubts of San Barbe and Grenada, covering the village and ridge of Sarre. In front of the right was the smaller Rhune, which was fortified and occupied by a brigade of Maransin’s division: a new redoubt with abbatis was also commenced to cover the approaches to the bridge of Amotz.
On the right of this line, beyond the bridge of Ascain, Daricau’s division of Clausel’s corps, and the Italian brigade of San Pol, drawn from Villatte’s reserve, held the intrenched camp of Serres; they thus connected Clausel’s position with Villatte’s, which crossed the gorges of Olette and Jollimont. Reille’s position, strongly fortified on the lower ground and partially covered by inundations, was nearly impregnable.
Soult’s weakest point was between the Rhune mountains and the Nivelle, where the space, gradually narrowing as it approached the bridge of Amotz, was the most open and the least fortified. The Nivelle, being fordable above this bridge, did not hamper the allies’ movements, and a powerful force acting in that direction could therefore pass by D’Erlon’s first line, and break between the right of his second line and Clausel’s left; it was thus Wellington framed his battle; for seeing the French right could not be forced, he decided to hold it in check while he broke their centre and pushed down the Nivelle to San Pé.
In this view, Hill, leaving four of Mina’s battalions to face the rocks of Mondarain, moved in the night by the passes of the Puerto de Maya to fall on D’Erlon.
On Hill’s left, Beresford was to send the third division against the unfinished redoubts and intrenchments covering the bridge of Amotz, thus turning D’Erlon’s right while it was attacked in front by Hill.
On the left of the third division, the seventh, descending from the Echallar pass, was to storm the Grenada redoubt, pass Sarre, and assail Clausel abreast with the third division.
On the left of the seventh, the fourth division, assembling on the lower slopes of the greater Rhune, was to descend upon San Barbe, and then, moving through Sarre also, to assail Clausel abreast with the seventh division.
On the left of the fourth division, Giron’s Spaniards, gathered higher up the flank of the great Rhune, were to move abreast with the others, leaving Sarre on their right. They were to drive the enemy from the lower slopes of the smaller Rhune, and then join the attack on Clausel’s main position. In this way Hill’s and Beresford’s corps, forming a mass of more than forty thousand infantry, were to be thrust on both sides of the bridge of Amotz, between Clausel and D’Erlon.
Charles Alten with the light division and Longa’s Spaniards, together eight thousand, was likewise to attack Clausel’s line on the left of Giron, while Freyre’s Gallicians approached the bridge of Ascain to prevent reinforcements coming from the camp of Serres. But ere Alten could assail Clausel’s right the smaller Rhune which covered it was to be taken. This outwork was a hog’s-back ridge, rising abruptly out of table-land opposite the greater Rhune and inaccessible along its front, which was precipitous and from fifty to two hundred feet high; on the enemy’s left the rocks gradually decreased, descending by a long slope to the valley of Sarre, and, two-thirds down, the 34th French Regiment was placed, with an outpost at some isolated crags between the two Rhunes. On the enemy’s right the hog’s-back sunk by degrees into an open platform, but was covered at its termination by a marsh scarcely passable. The attacking troops had therefore first to move against the perpendicular rocks in front, and then to file, under fire, between the marsh and lower rocks to gain an accessible point from whence to fight their way along the narrow ridge of the hog’s-back; the bristles of the latter being huge perpendicular crags built up with loose stones into small forts or castles which communicated by narrow foot-ways, and rose one above another until the culminant point was attained.