Chivalry, or the chivalric language, is an informal and varying code of conduct that developed in Europe between 1170 and 1220. It is associated with the medieval Christian institution of knighthood, with knights being members of various chivalric orders, and with knights' and gentlemen's behaviours which were governed by chivalrous social codes. The ideals of chivalry were popularized in medieval literature, particularly the literary cycles known as the Matter of France, relating to the legendary companions of Charlemagne and his men-at-arms, the paladins, and the Matter of Britain, informed by Geoffrey of Monmouth's Historia Regum Britanniae, written in the 1130s, which popularized the legend of King Arthur and his knights of the Round Table.