Indulgences and Holy Wars: The Revolutionary Impact of the First Crusade

On the 15th of July, 1099, over ten thousand Christian soldiers forced their way into the Holy City of Jerusalem. What was to follow was one of the most infamous massacres of the medieval period. Thirsty, hungry, and exhausted from 5 weeks of siege warfare, the Crusaders were utterly brutal in their treatment of the city’s Muslim population. The chronicler Raymond d'Aguilliers describes the sack which followed the Latin victory with nauseating piety and reverence: "Indeed, it was a just and splendid judgement of God that this place should be filled with the blood of the unbelievers, since it had suffered so long from their blasphemies. The city was filled with corpses and blood". 

The immense victory of the First Crusade was an event of revolutionary significance for medieval Christendom. This extraordinary march to Palestine simply should not have ended in victory. The seeming impossibility of a successful expedition to Palestine, crossing thousands of miles, gave the first crusaders an aura of divinity and piety; creating huge nostalgia and obligation among the next generation of Western nobility. As Riley-Smith has argued, failure would likely have renderedthe idea of armed pilgrimage to the Holy land illegitimate; its success appeared to all to be a manifestation of God’s will. Expeditions to the Holy Land and wars against the Muslims would be launched repeatedly over the following four centuries. The expense, distance and organisational complexity involved meant these ventures frequently ended in disaster; even leading to the sack of the great city of Constantinople in 1204. 

But the immediate consequences of the, mostly, shambolic expeditions which followed the First Crusade are only part of the story. Crusading became embedded into the fabric of Christendom; having a widespread effect on politics, religion and culture. It injected dynamism into the medieval political landscape. The incentive of remission of sins was a useful organising mechanism the papacy could use to wage war and achieve its political goals. Beginning with the monarchical Pope Innocent III, crusades became increasingly common against internal enemies. These not only included religious deviants, such as the Cathar heretics in southern France and the Pagans in the Baltic, but also political opponents, such as the Holy Roman Empire. As Norman Housley has argued, crusade preaching and the promise of salvation, was a hugely efficient way of gathering an army. 

The centuries long perpetuation of crusading was significant away from the battlefields and the bonfires of heretics. Holy War became an increasingly central component of noble identity. Stories of past crusade heroes were spread widely through literature, polemics and preaching. Crusading obligation was particularly strong in France. French monarchs were bestowed a special responsibility for crusading to the Holy Land, as to go on crusade gave one legitimacy among all aristocratic society. The rhythm of religious life also acquired a crusading tint. Tyreman finds that appeals to God for the recovery of the Holy Land became infused into the mass and other liturgy. Critically, the crusade indulgence gradually expanded into other areas of Christian life. Over the following centuries, the demand for remission of sins became increasingly monetised by religious authorities. The wealth accrued by papal institutions through these indulgences was pivotal in Martin Luther's break with the church in the early 16th century, and the beginning of the Reformation. The clear link to the Early-Modern period underlines the importance of the first use of the crusade indulgence. If the First Crusade suffered the excruciating failure which befell its successors, the cultural and political climate of Europe could have looked very different. 

Bibliography 

Primary Sources 

‘Raymond d’Aguiliere’s account of the siege of Jerusalem’, (1101), In: The Internet Medieval Sourcebook, [Accessed 6/03/2026]. 

Secondary sources 

Housley Norman, Contesting the Crusades, (Blackwell Publishing: 2006). 

Kostick, Conor, The Siege of Jerusalem: Crusade and Conquest in 1099, (Bloomsbury Publishing Plc: 2011). 

Riley-Smith, Jonathan, Oxford Illustrated History of the Crusades, (Oxford University Press; 1995). 

Rist, Rebecca, Papacy and Crusading in Europe, 1198-1245, (Continuum: 2009). 

Tyreman, Christopher, Gods War: A New History of the Crusades, (Penguin: 2006). 

Tyreman, Christopher, What the Crusades meant to Europe, In: Peter Linehan; Janet L. Nelson; Marios Costambeys (eds), The Medieval World, (Routledge Worlds: 2017), 146-159.