Jean De Joinville (1224-1317) was a French nobleman and knight, lord of the castle and territory of the same name. His memoirs are, in retrospect, an extraordinary historical document of the thinking of a man of his time and also a great source of information on the life of his king and personal friend: Louis IX of France, known as "the Saint" (1214-1270).

The saintliness of the French king—who was canonised in 1297 by Pope Boniface VIII—was so evident to his contemporaries that he was considered a saint even during his lifetime; a rare and unique case. "The king did not care about having a noble retinue, but preferred to be accompanied by the prayers and suffrages of the poor," Joinville recounted. This was due to his great devotion, his good and gentle nature, and, in particular, to certain actions believed only to be possible for a Saint (he was also granted miraculous powers). A promoter of major legislative activities, builder of fortifications, churches, and works of Christianization, Louis IX's activities were recounted with extraordinary precision by his knight and friend, who also followed him during the Sixth Crusade: a military expedition in which the king was also taken prisoner. Jean De Joinville recounts how, once shipwrecked in the Holy Land and taken prisoner by the Muslims, he and his men were forced to pay an exorbitant sum to free the Holy King and other knights. Once this sum was assembled, with considerable effort, and handed over to the infidels, King Louis was told that in reality a lower sum than agreed had been handed over, thus deceiving the enemy. Upon learning of this, the Capetian king was furious and ordered the remainder to be handed over, since lying, even to one's enemy after having given one's word, was unworthy of either a nobleman or a good Christian. Another day, after a battle, the crusaders' corpses were left rotting outside the camp, and no one wanted to deal with them. So King Louis himself set out with a shovel and a spade to give his men a dignified burial, arousing both excitement and admiration. Speaking of his men, Louis IX refused to leave the Holy Land after the poor progress of the Crusade because there was no way to "bring all his men home," demonstrating how much he cared more about the lives of thousands of people than his own.

Joinville himself would say of the king and his qualities that he was "the most beautiful knight I have ever seen."