<P> The crusaders consolidated their conquests into crusader states . During the 12th and 13th centuries, there were a series of conflicts between those states and the surrounding Islamic states . Appeals from those states to the papacy led to further crusades, such as the Third Crusade, called to try to regain Jerusalem, which had been captured by Saladin (d . 1193) in 1187 . In 1203, the Fourth Crusade was diverted from the Holy Land to Constantinople, and captured the city in 1204, setting up a Latin Empire of Constantinople and greatly weakening the Byzantine Empire . The Byzantines recaptured the city in 1261, but never regained their former strength . By 1291 all the crusader states had been captured or forced from the mainland, although a titular Kingdom of Jerusalem survived on the island of Cyprus for several years afterwards . </P> <P> Popes called for crusades to take place elsewhere besides the Holy Land: in Spain, southern France, and along the Baltic . The Spanish crusades became fused with the Reconquista of Spain from the Muslims . Although the Templars and Hospitallers took part in the Spanish crusades, similar Spanish military religious orders were founded, most of which had become part of the two main orders of Calatrava and Santiago by the beginning of the 12th century . Northern Europe also remained outside Christian influence until the 11th century or later, and became a crusading venue as part of the Northern Crusades of the 12th to 14th centuries . These crusades also spawned a military order, the Order of the Sword Brothers . Another order, the Teutonic Knights, although founded in the crusader states, focused much of its activity in the Baltic after 1225, and in 1309 moved its headquarters to Marienburg in Prussia . </P> <P> During the 11th century, developments in philosophy and theology led to increased intellectual activity . There was debate between the realists and the nominalists over the concept of "universals". Philosophical discourse was stimulated by the rediscovery of Aristotle and his emphasis on empiricism and rationalism . Scholars such as Peter Abelard (d . 1142) and Peter Lombard (d . 1164) introduced Aristotelian logic into theology . In the late 11th and early 12th centuries cathedral schools spread throughout Western Europe, signalling the shift of learning from monasteries to cathedrals and towns . Cathedral schools were in turn replaced by the universities established in major European cities . Philosophy and theology fused in scholasticism, an attempt by 12th - and 13th - century scholars to reconcile authoritative texts, most notably Aristotle and the Bible . This movement tried to employ a systemic approach to truth and reason and culminated in the thought of Thomas Aquinas (d . 1274), who wrote the Summa Theologica, or Summary of Theology . </P> <P> Chivalry and the ethos of courtly love developed in royal and noble courts . This culture was expressed in the vernacular languages rather than Latin, and comprised poems, stories, legends, and popular songs spread by troubadours, or wandering minstrels . Often the stories were written down in the chansons de geste, or "songs of great deeds", such as The Song of Roland or The Song of Hildebrand . Secular and religious histories were also produced . Geoffrey of Monmouth (d.c. 1155) composed his Historia Regum Britanniae, a collection of stories and legends about Arthur . Other works were more clearly history, such as Otto von Freising's (d . 1158) Gesta Friderici Imperatoris detailing the deeds of Emperor Frederick Barbarossa, or William of Malmesbury's (d.c. 1143) Gesta Regum on the kings of England . </P>

Belonging to or having to do with middle ages