At Clermont in November 1095 Urban II called on the knighthood of western Europe to march to the aid of the eastern Christians and recover Jerusalem — and got a far larger response than he had asked for.
On 27 November 1095, at the end of a church council at Clermont in the Auvergne, Pope Urban II preached a sermon in an open field outside the city to a crowd too large for the cathedral.
He called on the knights of the west to stop fighting each other and go to the aid of the eastern Christians, and to recover Jerusalem. He offered those who went the remission of penance for their sins.
The response exceeded anything he had planned for. Within four years an army had crossed Anatolia, taken Antioch and stormed Jerusalem — and the framework of holy war Urban improvised at Clermont shaped European politics for the next two centuries.
The immediate cause was a request from Constantinople. The Byzantine emperor Alexios I, rebuilding after the loss of Anatolia to the Seljuk Turks, sent envoys to a council at Piacenza in March 1095 asking for western mercenaries.
That is what he asked for and it is not what he got. Urban converted a request for troops into an armed pilgrimage under papal authority — a different thing entirely, with its own leadership, its own objectives and no obligation to serve a Greek emperor.
The papacy had its own reasons. Urban was in the middle of the Investiture Controversy with the German emperor, had a rival pope in Rome, and led a reform movement that had been trying for decades to direct aristocratic violence outward. A war fought at the pope's call, by an army that answered to a papal legate, answered several problems at once.
Five accounts of the sermon survive and no two agree. All of them were written after Jerusalem had fallen in 1099, by men shaping a speech to fit an outcome they already knew, and one of the five was not present.
What the versions share is a call to aid the eastern Christians, an account of atrocities against pilgrims, an appeal to knightly honour, and the offer of an indulgence. The cry "Deus vult" — God wills it — is reported as the crowd's response, and may well be the one detail everyone remembered accurately.
What is genuinely uncertain is how central Jerusalem was to what Urban actually said, as opposed to what the chroniclers put in his mouth once the city had been taken. Historians have argued the point for a century, and the archive states it as unresolved rather than picking a side.
Urban expected a disciplined force of knights departing the following August. What happened first was the People's Crusade: tens of thousands of poor pilgrims under preachers including Peter the Hermit, who left months early, massacred Jewish communities in the Rhineland on the way, and were destroyed by the Turks in Anatolia within weeks of crossing.
The pogroms of 1096 are the first mass violence against European Jewry of this kind, and they were carried out against the explicit instruction of local bishops, several of whom tried to shelter the communities and failed.
The princes' armies left in August 1096 as planned, under Raymond of Toulouse, Godfrey of Bouillon, Bohemond of Taranto and others — no king among them, and no single commander. They reached Constantinople, quarrelled with Alexios over oaths, crossed into Anatolia, took Antioch after an eight-month siege, and stormed Jerusalem on 15 July 1099.
Clermont created the crusade as an institution: a war with a papal indulgence attached, fought by volunteers who took a vow, with legal protections for their property while away. Every later crusade — to the Holy Land, against the Albigensians, in Iberia, in the Baltic — works within the framework improvised here.
It also permanently altered the relationship between eastern and western Christendom. Alexios asked for mercenaries and received an independent armed movement that founded its own states in territory he regarded as imperial; the mutual grievance that produced runs directly to the sack of Constantinople in 1204.
And the indulgence had consequences the reformers did not intend. The idea that an act could remit penance, and later that it could be extended and eventually purchased, is one of the threads that leads to the Reformation four centuries later.