Pedro II (1178-1213), known as “The Catholic”, was imbued with a profound religious devotion by his mother and saw his role as a knight champion of Christianity very much in that context. His generosity to the chivalric orders was prodigious. The Templars of Montpellier arranged for the marriage of the heiress of that city to Pedro who despite a marked attraction to women took a total adversion to his legitimate spouse, to the extent of refusing to consummate the marriage, and eventually seeking to divorce her. The marriage was in fact consummated as a result of trickery by the queen in an episode regarded by their ensuing son as a miracle.
Pedro made his way to Rome in 1204 to be solemnly crowned there by Innocent III. Meanwhile in Languedoc the Albigenisan heresy sprang up with the active support and participation of certain of the local rulers among whom Pedro had solemn allies and vassals. In order to defend them and in spite of his own orthodox beliefs, Pedro met the Catholic armies from northern France under Simon de Montfort before the castle of Muret and despite his own numerical superiority he lost the battle and his own life in the course of it. The infant son from the miracle of Montpellier, the great-grandson of Raymond and Petronila, who succeeded to the throne in 1213, was James I (King also in due course of Majorca and Valencia, Count of Barcelona and Urgell, Lord of Montpellier) known to history as “the Conqueror”.
In 1212 Peter he helped Alfonso VIII of Castile to defeat the Moors at Las Navas de Tolosa. This battle was the turning point in the history of Medieval Iberia. The forces of King Alfonso VIII of Castile were joined by the armies of his rivals, Peter II of Aragon and Alfonso II of Portugal to fight the Muslim Almohad rulers of the southern half of the Iberian Peninsula. Caliph al-Nasir led the Almohad army. The defeat of the Almohads signaled the beginning of a long decline in the power of the Moors in the Peninsula.
Following his performance against the Moors, Peter II was the most famous and respected crusader of the period. He had driven the Moslems from much of Spain, and won plaudits from the Papacy for his leadership. But Peter's problems had already started when the crusaders purported to replace Raymond-Roger Tranceval as Viscount of Carcassonne and Beziers in 1209. How could they do this? Feudal law was absolutely clear that it was for Peter as suzerain, to appoint, confirm and dispossess his own vassals - but now Innocent had a legal claim to be Peter's suzerain. Even the Northern Lords were uneasy about this precedent. As they clearly saw, if Innocent III got away with this then neither they nor any sovereign in Christendom would be safe.
Peter returned from Las Navas in the autumn of 1212 to find that in the course of the Cathar Crusade. Simon de Montfort had conquered Toulouse, exiling Raymond VI Count of Toulouse, Peter's vassal and brother-in-law. Peter crossed the Pyrenees and arrived at Muret in September 1213 to confront de Montfort's army. He was accompanied by Raymond of Toulouse, who gave Peter excellent counsel, to avoid battle and instead to starve out Montfort's forces. This suggestion was rejected as unknightly. Peter fought at the subsequent battle of Muret in 1213, but was killed during a needless show of bravado. (He was fighting in disguise - a common ploy for kings at the time and not apparently regarded as unknightly. A lowly vassal armed as the King of Aragon attracted the scorn of the Crusaders and Peter, unable to contain himself, shouted out something to effect of "here I am, come and get me".) He died, as brave as he was foolish at the hands of two French Crusader knights.
The death of the most famous Crusader in Europe, a King, surnamed the "Catholic", fighting against brother crusaders, shook both armies and indeed left the whole of Christendom horrified and bewildered.