Outside the town of Muret, south of Toulouse, a vastly outnumbered Catholic army under Simon de Montfort faced the army of King Peter II of Aragon, who had taken the side of the Cathar (Albigensian) heretics of southern France. The Catholic force was perhaps 1,000 cavalry against an allied army of some 30,000.
St. Dominic spent the night before the battle in the parish church of Muret leading a Rosary procession with the people of the town. The next day, in a sudden and lopsided victory, the Catholic cavalry shattered the Aragonese centre. Peter II was killed; the Cathar power in Languedoc was broken; the Rosary was popularly credited with the result. Dominic, who had been preaching against Albigensian dualism for years, made the Rosary the core meditative prayer of his new Order of Preachers — a tradition the Dominicans still bear.