The advance was then delayed, allowing the French, commanded by Marshal Nicolas Soult, to retreat to the River Nivelle. As Charles Esdaile says, ‘the reasons were political.’ The French had been cleared out of Iberia, apart from the blockaded and starving garrison of Pamplona, and some in Portugal and Spain were reluctant to participate in an invasion of France. There was also the risk that Napoleon would win his German campaign, allowing him to move huge number of reinforcements to the Franco-Spanish border.
Pamplona surrendered on 31 October, meaning that there was no justification for further delay. The political disputes were overcome, allowing Wellington to use his entire army offensively
The Nivelle itself was not a formidable obstacle, but it was overlooked by hills that had been fortified. Wellington decided to attack to the centre-left of the 20 mile long French position. An assault on the extreme French left was rejected because the mountain passes there were often blocked by snow in winter. The right flank, from the sea to the village of Ascain, was too strongly defended.
Wellington was aware that the French had a strong position, but believed that it could be taken. He told the senior officers of the Light Division that:
‘It appears difficult, but the enemy have not men to man the works and lines they occupy. They dare not concentrate a sufficient body to resist the attacks I shall make upon them. I can pour a greater force on certain points than they can concentrate to resist me.’
Sir John Hope was ordered to demonstrate between the coast and Ascain with 23,000 men in order to tie down an equal number of French troops. The main attack would come between Ascain and the Mondarrain mountain, where the 26,000 men of Sir Rowland Hill’s corps and the 29,000 of Lord Beresford’s corps would be opposed by 40,000 Frenchmen.
The key French position was a hill called the Lesser Rhune, separated from the Great Rhune, taken by the Allies just after they crossed the Bidassoa, by a ravine. The Light Division was selected to attack the Lesser Rhune. Success would expose the flanks of the French troops either side of it.
There were three separate enclosed fieldworks along the crest of the Lesser Rhune, and it appeared to be almost impregnable against an assault across the ravine from the Great Rhune. However, Wellington worked out a route that enabled the Light Division to descend into the valley and manoeuvre into a position to attack the Lesser Rhune’s flank. The fieldworks would not then be able to support each other against the attackers, and could be taken one after the other.
The Light Division began its attack before dawn, and had taken the Lesser Rhune by 8 am. The rest of the Allied army then advanced. The French were forced to retreat in order to avoid having their flanks turned.
The French lost 4,500 men killed, wounded and captured, plus 59 guns, and the Allies 2,700 men. The November day was short, and the onset of darkness probably saved the French from a disaster. Soult was able to establish a new line along the next river, the Nive.
 C. J. Esdaile, The Peninsular War: A New History (London: Allen Lane, 2002), p. 476.
 Quoted in J. Weller, Wellington in the Peninsula 1808-1814 (London: Greenhill, 1992), p. 320.
 Ibid., p. 325.