The Battle of Barrosa (Chiclana, 5 March 1811) was part of an unsuccessful manoeuvre to break the siege of Cádiz in Spain during the Peninsular War. During the battle, a single British division defeated two French divisions and captured a regimental eagle.
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 large Allied strike force was shipped south from Cádiz to Tarifa, and moved to engage the siege lines from the rear. The French, under the command of Marshal Victor, were aware of the Allied movement and redeployed to prepare a trap. Victor placed one division on the road to Cádiz, blocking the Allied line of march, while his two remaining divisions fell on the single Anglo-Portuguese rearguard division under the command of Sir Thomas Graham.
Following a fierce battle on two fronts, the British succeeded in routing the attacking French forces. A lack of support from the larger Spanish contingent prevented an absolute victory, and the French were able to regroup and reoccupy their siege lines. Graham's tactical victory proved to have little strategic effect on the continuing war, to the extent that Victor was able to claim the battle as a French victory since the siege remained in force until finally being lifted on 24 August 1812.
In January 1810, the city of Cádiz, a major Allied harbour and the effective seat of Spanish government since the occupation of Madrid, was besieged by French troops of Marshal Soult's I Corps under the command of Marshal Victor. The city's garrison initially comprised only four battalions of volunteers and recruits, but the Duke of Alburquerque ignored orders from the Spanish Junta and instead of attacking Victor's superior force, he brought his 10,000 men to reinforce the city. This allowed the city's defences to be fully manned.
Under pressure from widespread protests and mob violence the ruling Spanish Junta resigned, and a five-man Regency was established to govern in its place. 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. Additional troops continued to arrive, and by May, the garrison was 26,000 strong, while the besieging French forces had risen to 25,000.