On the morning of February 23rd 1814 the left wing of the Allied army under Sir John Hope began its daring but hazardous crossing of the Adour to the west of the town. The Coldstream and 3rd Foot Guards, supported by riflemen of the 5/60th, crossed the river in small groups, each party being ferried across the river in small rafts. By the end of the day a bridgehead was established and even a French counter-attack failed to stop the operation when a battery of rockets was scattered amongst them, sending the startled Frenchmen running for cover. By the afternoon of February 26th a bridge of boats had been constructed across the river, which enabled Hope to get some 8,000 men across to the north bank. Bayonne was now completely surrounded and the blockade of the town began.

The day after Hope's blockade began Wellington, with the main Allied field army, fought a major battle at Orthes, some thirty-five miles away to the east. On February 26th Beresford had crossed the Gave de Pau with the 4th and 7th Divisions near Peyrehorade, pushing Soult back towards Orthes. The 3rd Division forded the river at Berenx while Wellington himself brought up the 6th and Light Division, plus a force of cavalry, across on a pontoon bridge, which had been thrown across the Gave, also at Berenx. Hill, meanwhile, with the 2nd Division and Le Cor's Portuguese division, marched to the south of Orthes, passing to the east of the town but remaining on the south bank of the Gave.

On the morning of February 27th Wellington had with him on the northern bank of the Gave some 38,000 infantry and 3,300 cavalry as well as 54 guns. Soult's army, about 7,000 less with six fewer guns, occupied a strong position along a ridge which ran north from Orthes for about a mile before running west for three miles from the bend in the main Bayonne-Orthes road, which ran along the ridge, to the small village of St Boes upon which Soult rested his right flank.  Soult's troops occupied the whole length of this ridge from which three very prominent spurs extended south towards the Gave. The spur on the extreme western edge of the ridge does not actually connect with the ridge itself, being separated by a few hundred yards. The remains of an old Roman camp were situated on the forward edge of the spur and would feature prominently in the battle.

The battle opened shortly after 8.30am on the cold, frosty morning of February 27th when a battalion of French infantry was driven from the church and churchyard of St Boes by the 1/7th, 1/20th and 1/23rd, who made up Ross's brigade of the 4th Division. The brigade advanced further east along the ridge to clear the rest of the village but it came under fire from French artillery and could go no further. French troops under Taupin were then sent to recover the village and St Boes became the scene of severe house-to-house fighting as both sides struggled for its possession.

While the fight for St Boes flickered and flared Picton's 3rd Division entered the fray, attacking Soult's centre. His troops advanced up the two centre spurs but were held up by French artillery that swept the crests of the spurs, inflicting heavy casualties. The attack here was only intended to be a demonstration, however, and he pulled his troops back leaving just his strong skirmishing line of light troops and riflemen to prod and probe the French line, something which they continued to do for the next two hours.

Meanwhile, the fighting in St Boes intensified until at about 11.30 Wellington gave orders for an assault along the whole length of his line, leaving part of the Light Division only in reserve at the Roman Camp from where Wellington watched the progress of the fight.

On the Allied left Brisbane's brigade of the 3rd Division began to push its way up the eastern-most spur with the 6th Division following behind. At St Boes, the 4th Division was replaced by the 7th Division, while the 1/52nd advanced from the Roman camp to deliver an attack on the French brigade on the right flank of the advancing 7th Division.

These attacks were pressed home vigorously but French resistance was stiff and it was to take the advancing British columns about two hours of hard fighting to drive the French from the spurs. This was not accomplished without loss, particularly to the 1/88th, three companies of which suffered heavy losses when a squadron of French cavalry, the 21st Chasseurs, charged and overran them after catching them in line. The French cavalry suffered similarly when they received the return fire from Picton's men, half of their number being killed or wounded.

The French troops along the ridge were being severely pushed by Wellington's attacking columns but it was the advance by the 1/52nd, under Colborne, that decided the day. This battalion entered the fight in support of the Walker's 7th Division just at the moment when this division, along with Anson's brigade of the 4th Division, was finally driving the French from the body-choked village of St Boes. The 52nd advanced almost knee-deep in mud in places but when it reached the crest of the spur it took Taupin's division in its left flank. Taupin's men were driven back by Colborne's determined charge and fell in with those retreating from St Boes. In so doing, they precipitated a degree of panic, which caused the collapse of the entire French right. It was now about 2.30pm and with Wellington's triumphant troops pouring along the main road on top of the ridge the day was as good as won.

At first, Soult's army began to fall back in an orderly manner with the divisions of Villatte and Harispe drawn up on his left flank to cover the withdrawal. However, Hill's corps had crossed the Gave to the east of Orthes and fell upon Harispe's division, driving it back upon Villatte. The controlled retreat soon became a panic-stricken flight, which spread along the whole of the French line, Soult's men discarding great loads of equipment to facilitate their retreat to the north-east towards Toulouse.