Cádiz had been invested by the French in early 1810, leaving it accessible from the sea, but in March of the following year a reduction in the besieging army gave its garrison of British and Spanish troops an opportunity to lift the siege.

[a] The Regency, recognising that Spain could only be saved with Allied aid, immediately asked the newly ennobled Arthur Wellesley, Viscount Wellington, to send reinforcements to Cádiz; by mid-February, five Anglo-Portuguese battalions had landed, bringing the garrison up to 17,000 men and making the city effectively impregnable.

[11] Joined by a composite battalion of flank companies under Colonel Browne, the troops marched to Tarifa on 24 February, where they received further reinforcement from the fortress garrison there.

[12] By 27 February, they were joined by la Peña's Spanish troops, who had left Cádiz three days after Graham and, despite encountering similar weather difficulties, had succeeded in landing at Tarifa.

Unaware of the delays in sailing, Begines had advanced as far as Medina-Sidonia in search of the Allied army; unsupported, and embroiled in skirmishes with Victor's right flank, he returned to the mountains.

[13] Having concentrated, the combined Allied force began marching north towards Medina-Sidonia on 28 February, and la Peña now ordered Begines's irregulars to join them at Casas Viejas.

Rather than engaging the French and forcing Victor to weaken his siege by committing more of his troops to the town's defence, la Peña decided that the Allied army should march across country and join the road that ran from Tarifa, through Vejer and Chiclana, to Cádiz.

[14] This change of plan, combined with further bad weather and la Peña's insistence on marching only at night, meant the Allied force was now two days behind schedule.

Victor could not allow the Cádiz garrison, which still numbered about 13,000 men, to make a sortie against his lines while he was threatened from outside, so on the night of 3–4 March he sent six companies of voltigeurs to storm the bridgehead entrenchments and prevent a breakout.

[c] Marshal Victor had, by now, received intelligence from a squadron of dragoons that had been driven out of Vejer, informing him of the strong Anglo-Portuguese and Spanish force making its way up the western road from Tarifa.

[15] General Eugène-Casimir Villatte's division was sent to block the neck of the peninsula on which the western road ran, preventing access to the Santi Petri creek and the Isla de Léon.

With the aid of a fresh sortie of Zayas's troops from Cádiz, and reinforced by a brigade of the Prince of Anglona's division, the Spanish drove Villatte's force across Almanza Creek.

In addition, three Spanish and two King's German Legion (KGL) squadrons of cavalry, under the command of Colonel Samuel Whittingham, were sent to flank this rearguard force on the coast track.

[20] He could see that the bulk of the Spanish troops had taken station opposite Villatte and, on hearing reports that Barrosa Ridge was deserted, realised that here was an opportunity to take this commanding position.

[21] Meanwhile, midway through his march to join la Peña's Spaniards, Graham received news from Spanish guerrilleros that French soldiers had emerged from the Chiclana forest.

These were prime targets for shrapnel rounds fired by the ten cannon under Major Duncan which, having made rapid progress through the woods, arrived in time to support the skirmish line.

Leval's men then encountered Bushe's companies of the 20th Portuguese, who supported the light battalion's retreat and kept the French engaged until Wheatley's brigade had formed up in line on the edge of the woods.

The capture of the eagle—the first to be won in battle by British forces in the Peninsular wars—cost Ensign Keogh of the 87th his life and was finally secured by Sergeant Patrick Masterson[29] (or Masterman, depending on source).

The Marshal deployed two or three relatively unscathed battalions to cover the reorganisation of his forces and secure their retreat, but Graham had also managed to call his exhausted men to order and he brought them, with Duncan's artillery, against Victor's new position.

He learnt of the French advance at about the same time as Graham, and decided to entrench his full force on the isthmus defending the approach to the Isla de Léon.

Fully expecting a renewed offensive, Victor had made plans to stall any Allied advance just long enough to blow up most of the besieging forts and to allow I Corps to retreat to Seville.

[35] La Peña had determined not to heed plans from Graham and Admiral Keats to make a cautious advance against the French at Chiclana, and he even refused to send out cavalry scouts to find out what Victor was doing.

After remaining entrenched at Bermeja during 5–6 March, the Spanish army crossed to the Isla de León the following day, leaving only Beguines's irregulars on the mainland.

[35] It would remain so for another eighteen months, until finally being abandoned on 24 August 1812, when Soult ordered a general French retreat following the Allied victory at Salamanca.

[37] At a time when Anglo-Spanish relations were already strained, Graham's criticism of his Spanish allies meant that it was no longer politic for him to remain in Cádiz, so he was transferred to Wellington's main army.

[m] Strategically, however, the failure of the Allies to follow up their victory allowed Victor to reoccupy his siege lines; Cádiz was not relieved and the campaign effectively failed to achieve anything.