In 1147, as part of the Reconquista, crusader knights led by Afonso I of Portugal besieged and conquered Lisbon. The city, with around 154,000 residents at the time, was returned to Christian rule. The reconquest of Portugal and re-establishment of Christianity is one of the most significant events in Lisbon's history, described in the chronicle Expugnatione Lyxbonensi, which describes, among other incidents, how the local bishop was killed by the crusaders and the city's residents prayed to the Virgin Mary as it happened. Some of the Muslim residents converted to Roman Catholicism, and many of those who did not convert fled to other parts of the Islamic world, primarily Muslim Spain and North Africa. All mosques were either destroyed or converted into churches. As a result of the end of Muslim rule, spoken Arabic gradually lost its place in the everyday life of the city and disappeared altogether.
The first Portuguese university was founded in Lisbon in 1290 by King Denis I; for many years the Studium Generale (General Study) until it was installed permanently in Coimbra
During the last centuries of the Middle Ages, the city expanded substantially and became an important trading post with both Northern European and Mediterranean citie