On the French side each lieutenant-general had a special position to defend. D’Erlon’s first line, its left resting on the fortified rocks of Mondarin which could not be turned, run from thence along the Choupera and Atchuleguy mountains by the forge of Urdax to the Nivelle. This range was strongly entrenched and occupied by one of Abbé’s and one of D’Armagnac’s brigades, Espelette being behind the former and Ainhoa behind the latter. The second line or main position was several miles distant on a broad ridge, behind Ainhoa, and it was occupied by the remaining brigades of the two divisions. The left did not extend beyond the centre of the first line, but the right reaching to the bridge of Amotz stretched with a wider flank, because the Nivelle flowing in a slanting direction towards the French gave greater space as their positions receded. Three great redoubts were constructed in a line 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, Clauzel’s position extended to Ascain, also 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 the range to Ascain, both flanks rested alike upon that river, having communication by the bridges of Amotz and Ascain on the right and left, and a retreat by the bridges of San Pé and Harastagui which were in rear of the centre. Two of Clauzel’s divisions reinforced by one of D’Erlon’s under general Maransin were here posted. In front of the left were the redoubts of St. 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 belonging to Clauzel’s corps, and the Italian brigade of San Pol drawn from Villatte’s reserve, were posted to hold the entrenched camp of Serres and to connect Clauzel’s position with Villatte’s, which was as I have before said on a ridge crossing the gorges of Olette and Jollimont. The French right wing under Reille, strongly fortified on the lower ground and partially covered by inundations, was nearly impregnable. Soult’s weakest point of general defence was certainly the opening between the Rhune mountains and the Nivelle. Gradually narrowing as it approached the bridge of Amotz this space was the most open, the least fortified, and the Nivelle being fordable above that bridge could not hamper the allies’ movements. Wherefore a powerful force acting in this direction could pass by D’Erlon’s first line and breaking in upon the main position, between the right of that general’s second line and Clauzel’s left, turn both by the same attack.