General Graham resolved to make an effort to raise the siege by attacking the rear of the besieging army, and in February 1811, he sailed from Cádiz with a force of upwards of 4,000 men, accompanied by 7,000 Spanish troops, under General La Pena, to whom, for the sake of unanimity, the chief command was conceded. The allied troops assembled at Tarifa, in the Straits of Gibraltar, and, moving northward, they arrived, on the morning of 5 March, at the heights of Barrosa, which were on the south of Cádiz and of the lines of the besieging army.