[3] The arrival of a relief army, under King Philip IV of Spain's favorite don Luis de Haro in October, lifted the siege.

[7] San Lorenzo was then dismissed from his command and replaced by dom Joanne Mendes de Vasconcelos, who easily managed to retake both Mourão and Olivença in the following months, since their Spanish garrisons had been considerably diminished in order to move troops to face the French armies in Catalonia.

The military governor of the fortress was the Marquis of Lanzarote, Diego Paniagua y Zúñiga,[9] but the command of the army belonged to the Duke of San German, who had retreated to Badajoz after the loss of Olivenza, which he had briefly attempted to retake.

[9] The defenses of the town consisted essentially of an old Moorish Alcazaba and a medieval wall dating from the Almohad period, reinforced since the outbreak of the war in 1640 by various newly built bulwarks and ravelins.

[2] Mendes de Vasconcelos arrived shortly thereafter with the main Portuguese army, with its artillery, and a large number of supply wagons brought from Elvas.

[12] The garrison suffered from a lack of ammunition and supplies, the soldiers were dressed in rags or were practically nude, and there was none among the civilian population of the town trained to wield a weapon.

Mendes de Vasconcelos had decided, in a war council with many other senior officers, to attack Fort San Cristóbal, a key point in the Badajoz defenses.

The plan was for six Portuguese squadrons under dom João da Silva to block the entrance to the bridge, isolating the redoubt from Fort San Crisóbal.

[2] Maestre de Campo dom Diogo Gomes was given the task of cutting the communication lines along the Guadiana river and Pedro Almado of distracting several minor forts nearby.

After twenty-two days of prolonged action, during which the defenders, led by the Marquis of Lanzarote, virtually wiped out Almado's regiment with musketry fire and firebombs, Mendes de Vasconcelos ordered a withdrawal.

[16] The Portuguese general, convinced of the impossibility of taking Badajoz by assault, changed his strategy and began a circumvallation of the town,[15] in order to try to isolate it completely.

[20] On 20 June, after an ineffective bombardment by a 6-gun battery put in place to try to breach the parapets, the Portuguese tercios and the cavalry, the latter covered by ranks of musketeers, were ordered to attack.

[19] No significant action took place during this period, except for an ambush near San Gabriel by André de Albuquerque, against a Spanish supply convoy sent from La Albuera,[25] and various sorties by the garrison of Badajoz to try to obstruct the Portuguese works.

[27] On 6 August, however, Osuna and San German abandoned the town, and with 1,200 cavalry soldiers, broke the lines of circumvallation near the quarter of Santa Engracia, between two Portuguese redoubts, reaching Alburquerque shortly thereafter.

[29] The Spanish concentrated their efforts on the defense of a large ravelin in Pradaleras garrisoned by 2,000 infantry and 1,000 cavalry, against Portuguese artillery fire from Cerro del Viento and San Miguel.

[31] The Duke of Medina de las Torres had suggested that Philip IV himself should lead the relief of Badajoz in the company of all the Grandees of Spain.

[32] Luis de Haro, Philip IV's favourite, however, feared that Queen Mariana of Austria would be given the government of the country during the absence of the king, and, although having no military experience, offered himself to lead the relief army.

[31] The buildings in Cerro del Viento were set on fire and the bridge over the Gévora river was destroyed,[31] The Portuguese army retreated unmolested to Elvas having lost 6,200 men in all,[3] either killed in battle or dead from disease.

[32] When the Spanish relief army arrived, Luis de Haro entered Badajoz, where he was acclaimed by some as "Liberator of the town and Restorator of the Monarchy".