Urban II's Call at Clermont

Pope Urban II preached the crusade at the Council of Clermont on 27 November 1095, responding to an appeal from the Byzantine Emperor Alexios I Komnenos for military help against the Seljuk Turks, who had taken most of Byzantine Anatolia after their victory at Manzikert in 1071. Urban's sermon, known only through later and not entirely consistent reports, called on Western knights to set aside the private warfare that consumed so much of their energy at home and turn it instead toward liberating the Christians of the East and recovering Jerusalem, offering those who went a remission of the penance owed for their sins.

The response outran anything Urban had organized for. An unarmed and poorly provisioned popular movement under preachers including Peter the Hermit set out ahead of the main armies in what is remembered as the People's Crusade, and was destroyed by the Seljuks in Anatolia within months. The main crusader armies, drawn from France, Flanders, southern Italy and beyond, assembled separately through 1096 and 1097 and converged on Constantinople, where Alexios required their leaders to swear an oath to return any former Byzantine territory they recaptured to the empire, a promise that later became a major source of Byzantine-Latin friction.