The traditional number of peers is twelve. They are:  According to Matthew Paris, the Duke of Normandy and Duke of Aquitaine ranked above the Duke of Burgundy. But since the first two were absorbed into the crown early in the recorded history of the peerage, the Duke of Burgundy has become the premier lay peer. In their heyday, the Duke of Normandy was undoubtedly the mightiest vassal of the French crown. The constitution of the peerage first became important in 1202, for the court that would try King John of England in his capacity as vassal of the French crown. Based on the principle of trial by peers, a court wishing to acquire jurisdiction over John had to include persons deemed to be of equal rank to him in his capacity as either Duke of Aquitaine or Normandy. None of the peers had been specified, but since John's trial required the presence of the peers of France, it can be said that the first two peerages identifiable in the documents would be the duchies of Aquitaine and Normandy. In 1216, Erard of Brienne claimed the County of Champagne through the right of his wife, Philippa of Champagne. Again this required the peers of France, so the County of Champagne is also a peerage. Six of the other peers were identified in the charter — the archbishop of Reims, the bishops of Langres, Chalons, Beauvais and Noyon, and the Duke of Burgundy. The tenth peerage that could be identified in the documents is the County of Flanders, in 1224. In that year John de Nesle entered a complaint against Joan of Flanders; the countess responded that she could only be cited by a peer. The absence of the two remaining peers in the documents of this era can be explained thus: the bishop of Laon had only been recently elected at the time the other ecclesiastical peers were mentioned, in 1216, and probably not yet consecrated; the Count of Toulouse, on the other hand, is a heretic. Thus, though there had been differences in the dates of the identification of the twelve peers, they were probably instituted simultaneously and their identities were known to their contemporaries. These twelve peerages are known as the 'ancient peerage' or ', and the number twelve is sometimes said to have been chosen to mirror the twelve paladins of Charlemagne in the ' (see below). Parallels may also be seen with the mythical Knights of the Round Table under King Arthur.