Pope Urban II delivered the sermon at the Council of Clermont in France that launched the First Crusade, promising spiritual rewards to those who took up arms for the faith. This event marked a shift in the relationship between the papacy and secular rulers and established the concept of holy war in Christian thought. The speech, though not recorded verbatim, became iconic in Christian history and literature.

Urban II's sermon inspired the crusade epic tradition and the fusion of religious devotion with martial valor in Christian poetry. The council's rhetoric of holy war influenced the development of the chanson de geste and the religious verse of the High Middle Ages, from the Cantar de mio Cid to the poetry of the crusading orders.