After centuries of domination by laypeople (872-1046), at the Synod of Sutri in 1046 the westerm Catholic church broke free and a new Pope was installed, Clement II. After a succession of similarly reforming popes, in 1073 the Benedictine monk, Hildebrand, part of the Cluny movement for monastic reform, became Pope Gregory VII. He continued the trend towards centralisation in the name of reform, declaring the pope as universal bishop and vicar of St Peter (Dictatus Papae, 1075) and purging the church of simony (church positions being bought) and sexual immorality among the clergy. Gregory VII's face-off with western Emperor Henry IV, temporarily led to the latter's humiliation, but eventually led to the Pope spending his final years in exile. The longstanding controversy over lay investiture was finally resolved at Worms in 1122, at which it was agreed that the secular power conferred only secular benefits on clerics, while spiritual power lay with the church. The height of papal power and centralisation came under Innocent III, who presided at the 1215 Council (Lateran IV), which proclaimed the Pope to have "plenitude of power"; all power, spiritual and also secular, allegedly derived from the Pope, the "Vicar of Christ".
Meanwhile, from the time of Pope Urban II (1098), the Western Catholic Church sponsored Crusades, successive military campaigns to reclaim the Holy Sites of Christendom from Muslim control. In 1204 the Fourth Crusade led to the sacking of Eastern Orthodox Christian Constantinople and its occupation by the western powers, established a Western Catholic Patriarch. This act finalised the schism of 1054 between the western Catholic church of Rome and the eastern Orthodox Church in Constantinople. Crusades were also directed towards pagans (Northern Crusades) and heretics, such as the Cathars. Later Gregory IX set up the Inquisition (literally: "Interrogation") as means of combating heresy. An alternative, more irenic, non-coercive approach was adopted by preaching orders such as the Dominicans, and western missionaries to Muslims, such as Francis of Assisi and Raymond Lull (see also below).
The Cistercian movement, founded in 1097, rekindled the reforming zeal of the earlier Cluny monastic reform movement begun in 910. The most famous Cistercian monk was Bernard of Clairvaux (1090-1153), a monk, mystic, preacher and Bible scholar. Another centre of Christian mysticism at the time was the Abbey of St Victor.
A new impetus in the western church came from various grass-roots movements aiming to get back to the "apostolic life" of the New Testament: simplicity, mission and poverty. An early example were the Poor of Lyons, began by Valdo (hence "Waldensians") from around 1173. This movement was rejected by the church and became a proto-Protestant church, which in the 16th century joined the Reformation. However, later similar movements, such as those began by Francis of Assisi and Dominic Guzman, were given papal blessing and became new mendicant monastic orders (Franciscans and Dominicans, respectively). Other mendicant orders formed somewhat later included the Carmelites (1247).
The 13th century was also a time of architectural and academic achievement. The Cathedral of Saint Denis, Paris, completed in 1144, became a model for what was later referred to as 'Gothic' style of church architecture ("opus Francigenum"), symbolising the medieval dominance of Christianity and its striving heavenwards. Arguably one of the greatest examples of Gothic architecture is the cathedral at Chartres (picture). At the recently founded universities, following earlier thinkers such as Anselm (1033-1109), Albert the Great, Thomas Aquinas and other scholastics systematised Christian thinking, inspired by ancient Greek philosopher Aristotle. A motto of scholasticism was "faith seeking understanding".
After a long period of decline following the death of Innocent III in 1216, under Pope Boniface VIII the emerging Kingdom of France, under Philip the Fair, overcame, leading to the election in 1305 of French Pope Clement V, who never stepped foot in Rome and eventually set up his residence in Avignon from 1309 - the start of the so-called Babylonian captivity of the western church (1309-1377).
