The Reform movement took place during the 11th century. It originated in Cluny, a monastery in Burgundy:
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Cluny monastery was founded in 909 by William the Pious, Duke of Aquitaine. The monastery was thought to be the largest of the time, and is reconstructed below:
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The monastery also became the grandest, most prestigious and best endowed monastery of the time, with great Romanesque architecture, as can be seen below in the ground plan of the Basilica:
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The monastery at Cluny became famous thanks to a well developed administrative structure, and a sequence of highly competent abbots. It expanded, and eventually became acknowledged leader of western monasticism.
Cluny was able to expand as other monasteries who wished to learn from it were encouraged to follow exactly the same rules, and therefore Cluny expanded into a network of related houses, where it was eventually agreed that Cluny should have superiority over the others, along with powers of appointment.
By the 11th Century there were more than 1000 monasteries following the Cluniac version of Benedictine rule.The purpose of Cluny was to bring the clergy back to the regulations, and to re-establish discipline in convents. Cluny aimed to restore the ancient regulations of St Benedict to vigour by the practice of labour, obedience and poverty, and after reforming monasteries, the monks still remained Benedictines. It was decided, as mentioned above, that the reformed Cluny monastery should direct all convents founded or reformed by it, and thus Cluny became the head of the order, and the reformed Cluniac convents became priories, rather than abbeys, and all obeyed the same abbot, and sent delegates to the general assemblies of the Cluniac order.
The monks of the Cluny obliged the rest of the clergy to reform their manners, and supported the Pope and brought all Christians, laity and clergy, to submit to his authority. Pope Gregory VII (seen in greater detail below), a papal reformer and ruler, was a Cluniac monk.

Papal Reform was another way in which changes were made in the way that ecclesiastical authority was recognised. A series of Popes, including Leo IX, Gregory VII and Calixtus II worked to reform the election of Church authority by stamping out simony (the practice of buying Church offices) and enforcing celibacy for all priests (eliminating heirs to whom power could be passed down). In addition to these reforms, the Church sought to establish itself as a seperate spiritual authority superior to that of various European monarchs.
Firstly, Leo IX, building on reforms that helped to restore order within the monastic tradition (such as the Cluniac reforms), began his reign by promoting clerical celibacy and outlawing simony. A quick succession of Popes continued these reforms and in 1059 Pope Nicholas II convened a synod at Lateran Cathedral at Easter where it was determined that the election of Popes would rest with the cardinals, thus removing the authority of appointment from Holy Roman Emperors.
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Gregory VII was made Pope on April 22nd 1073 and died in 1085. He believed that he was sent to Earth to transform Christendom by seizing absolute control of ecclesiastical affairs. He continued reforms against simony and successfully promoted clerical celibacy in England. However, he met with stiff resistance from Philip I in France and Henry IV in Germany. With Philip's support, the French clergy refused to agree to Gregory VII's reforms. In Germany, Henry IV continued to exert influence in the election of Church leaders loyal to him, and to plunder and destroy churches in open conflict with the Holy See. In response to this, GregoryVII excommunicated Henry IV twice from the Church and released his subjects from their oath of allegiance. Henry IV led a military campaign against Pope Gregory which led to his death in exile in 1085
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Gregory VII and Crusades: Gregory VII believed in Holy War - the idea that sanctified violence would actually help cleanse a warrior's soul of sin. This shows that the Papacy was opening up a new path of salvation for its Latin followers. Gregory VII also believed in the Just War Theory, created by St Augustine, which was the theory that a war could be lawful and justifiable if fought under strict conditions, and started by a legitimate authority. It also had to be fought for a just cause and with right intention (and least violence). The Just War theory is also known as bellum iustum.
Gregory VII argued that all lay society had the obligation to defend the Latin Church as 'soldiers of Christ' through physical warfare. In 1074 he tried to start a holy war in the eastern Mediterranean in aid of the Greek Christian Orthodox Church, by calling for up to 50,000 soldiers, however this was not successful, perhaps only due to the hardships that Gregory VII endured in his disputes with secular authorities and King Henry IV. Without such distractions, Gregory VII likely would have called the first Crusade in 1074. In the 1080s, he wrote that all his supporters should fight the Emperor and face "the danger of the coming battle for the remission of all their sins".

Following the brief three year reign of Pope Victor III, Otho of Lagery became Pope Urban II in 1088.

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Pope Urban II was Gregory VII's old advisor, and his successor. He would preach the first Crusade. He was born into a knightly family in the province of Champagne in 1042. While a young man he became a Canon and archdeacon in Reims. In 1070 he retired to Cluny Monastery. There he fell under the guidance of St. Hugh who sent him to Rome to serve under Pope Gregory II. One of his first acts as Pope was to call on the Princes and nobility that had been loyal to Gregory VII to remain loyal to him as he would hold fast to his policies and ideology. In the 1090s, when Urban II was Pope (he himself was a Cluniac monk), the Cluniac Reform Movement was reaching an apex. He was also in favour of Holy Wars, however his ideas appeared moderate in comparison to Gregory VII and therefore he received less criticism. After spending the first half of his reign dealing with political division and war in Italy, the Pope was able to enter Rome only 3 years after the start of his papacy, he then finally turned his attention to events in the East.
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In Pope Urban II's Sermon of Clermont on 27th November 1095, he declared that Christendom was in dire trouble and that the Holy City of Jerusalem was now in the hands of Muslims - "a people ... alien to God". To the Christians of the West, who had little experience of other faiths, the Muslims seemed non-human savages, and seemed 'demonised'. He preached to the people in their own language, and requested that the people went on a Crusade to liberate Jerusalem, and promised that those brave and devoted Christians willing to go to the aid of Eastern Christians would have a plenary indulgence and he extended the Truce of God to assure the nobility that their lands and other property would not suffer from attacks at home while they were away. The Pope's words stirred knights reared in a culture of militant Christianity and they answered the Pope's call for an armed pilgrimage to the Holy Land with shouts of "Deus lo volt!" or "God wills it!". The Pope then made his way through France and Italy preaching the Crusade, as clerics throughout Latin Christendom joined in Urban's successful efforts in preaching what would become known as the First Crusade.