The siege of Lisbon, from 1 July to 25 October 1147, was the military action against the Muslim-ruled Taifa of Badajoz that brought the city of Lisbon under the definitive control of the new Christian power, the Kingdom of Portugal.
The siege of Lisbon was one of the few Christian victories of the Second Crusade—it was "the only success of the universal operation undertaken by the pilgrim army", i.e., the Second Crusade, according to the near contemporary historian Helmold, although others have questioned whether it was really part of that crusade. It is seen as a pivotal battle of the wider Reconquista.
The fall of Edessa in 1144 led to a call for a new crusade by Pope Eugene III in 1145 and 1146. In the spring of 1147, the Pope authorized the crusade in the Iberian Peninsula. He also authorized Alfonso VII of León and Castile to equate his campaigns against the Moors with the rest of the Second Crusade. In May 1147, a contingent of crusaders left from Dartmouth, Devon in the Kingdom of England. They had intended to sail directly to the Holy Land, but weather forced the ships to stop on the Portuguese coast at the northern city of Porto on 16 June 1147. There they were convinced to meet with Afonso I of Portugal, who had in 1139 declared himself king of the new Kingdom of Portugal.
The crusaders agreed to help the King attack Lisbon, with a solemn agreement that offered to the crusaders the pillage of the city's goods and the ransom money for expected prisoners. The siege began on 1 July. The city of Lisbon at the time of arrival consisted of sixty thousand families, including the refugees who had fled Christian onslaught from neighbouring cities of Santarém and others. Also reported by the De expugnatione Lyxbonensi is that the citadel was holding 154,000 men, not counting women and children; as the medieval account put it, after 17 weeks of siege "the inhabitants were despoiled and the city cleansed".
The rulers of Lisbon agreed to surrender on 24 October, four months later, primarily because of hunger within the city. Most of the crusaders settled in the newly-captured city, but some of the crusaders set sail and continued to the Holy Land. Lisbon eventually became the capital city of the Kingdom of Portugal in 1255.
Second Crusade
The traditional start of the Reconquista is identified with the defeat of the Muslims in the Battle of Covadonga in 722. After the First Crusade in 1095–1099, Pope Paschal II urged Iberian crusaders (Portuguese, Castilians, Leonese, Aragonese, and others) to remain at home, where their own warfare was considered just as worthy as that of crusaders travelling to Jerusalem.
In 1142, during the siege of Lisbon (1142), Afonso Henriques, taking advantage of the passage of a group of Anglo-Norman crusaders on their way to the Holy Land, attempted to use them to take the Muslim-ruled city of Lisbon. Although this attempt ultimately failed leaving some distrust among the crusader forces, it showed the Portuguese monarch the usefulness of such force in future attempts.
The fall of Edessa in 1144 led to a call for a new crusade by Pope Eugene III in 1145 and 1146. In the spring of 1147, the Pope also authorized a crusade in the Iberian peninsula, where "the war against the Moors had been going on for hundreds of years." Pope Eugene encouraged Marseilles, Pisa, Genoa, and other Mediterranean cities to fight in Iberia. He also authorized Alfonso VII of León and Castile to equate his campaigns against the Moors with the rest of the Second Crusade.
On 19 May 1147, a contingent of crusaders left from Dartmouth in England, consisting of crusaders from Flanders, Frisia, France, England, Scotland and some German polities who collectively considered themselves "Franks". No prince or king was in charge of the expedition, and its participants seem to have been largely made up of townsmen, who organised themselves using a sworn oath. Leadership was provided by Hervey de Glanvill, Constable of Suffolk. Other crusader captains included Arnout IV, Count of Aarschot leading the Rhinelanders, Christian of Gistel leading the Flemish and Boulogne forces, and the Anglo-Norman forces led by Simon of Dover, Andrew of London, and Saher of Archelle. Important decisions were made collectively by the commanders.