The Spanish began the siege by digging a line that was only a semicircle and did not completely incircle the city. The attack was concentrated between the
Santa Cruz and
São João bastions. The Spanish aimed a battery of 24 cannons and another of 4 cannons and 11 mortars at this spot. At the
Santa Cruz bastion, the Portuguese held 2 cannon, 11 mortars and 2 bomb mortars, while at
São João they had 3 pieces. To the right of the São João bastion, at the
Bixa Torta bastion, there were 4 more cannons. In addition, the moat had been flooded by the population. The artillery bombardment spread terror throughout the town and the women took refuge in the monasteries, but despite the severity of the attack, the defence was equally fierce and the rest of the population, the engineering and artillery officers and the governor remained in high spirits. As the artillery bombardment continued, Portuguese soldiers and guerrillas harassed the Spanish lines, carrying out cavalry sorties, raids and counter-mining operations. A breach was eventually opened in the bastion of
São João and on 25 October the Spanish prepared to storm through it, but the Portuguese lit on it a large fire that blocked the passage. On the 27th, 700 men in reinforcements commanded by the
Count of Ericeira Luís Carlos Inácio Xavier de Meneses and General Paulo Caetano de Alburquerque entered Campo Maior after skirmishing with the besiegers. The Spanish attempted to take Campo Maior by storm twice under the command of Lieutenant General Pedro de Zuñiga, but were repelled with heavy losses. The general then requested an armistice to recover the dead and wounded. Although the Spanish managed to breach the
São João bastion and capitulation was imminent, the remarkable resistance of the defenders forced the Spanish to withdraw after a month due to exhaustion and lack of progress. ==Aftermath==