The battle of Bornos (1 June 1812) was a French victory over the Spanish army of General Ballasteros, who had been asked to carry out a diversion to prevent Soult from sending troops north to interfere with Wellington's advance on Salamanca.
In the spring of 1812 Ballasteros had conducted a successful campaign, but had then been pursued by strong French columns and had retreated to Gibraltar. By May the French had been forced to retreat from the area, freeing Ballasteros to resume his campaign. Wellington had asked him to carry out some sort of diversion to keep Soult pinned down in the south, and he chose to attack General Conroux, who had 4,500 men at Bornos (9th Leger, 96th Ligne, one battalion from 16th Leger and 5th Chasseurs), covering the rear of the French siege lines at Cadiz.
Ballesteros had 8,500 infantry and a small force of cavalry. He decided to launch a surprise attack on Conroux, and arrived at Bornos early on 1 June under cover of a heavy mist. He launched a surprise attack on the French positions, and at first was very successful. However Conroux was able to restore order in his army. First he rallied, and then he launched a counterattack that forced Ballasteros to retreat across the Guadalete.
Ballasteros still outnumbered the French (he lost 1,500 men in the fighting, the French 400, so Ballasteros still had 7,000 men, the French 4,000) and was seriously considering launching a counterattack when reinforcements began to reach the French. Ballasteros decided to retreat to Ubrique. However Soult had detached six battalions of infantry and two cavalry regiments to stop him, and so he was forced to retreat back to his camp at Gibraltar.
Soult was unable to concentrate against Ballasteros, as an Anglo-Portuguese force under General Hill was now threatening his lieutenant on the Portuguese frontier, General Drouet. Soult detached part of his field army to support Drouet, but refused to help Marmont during the Salamanca campaign.