Louis IX of France

The Latin empire that western crusaders had set up at Constantinople in 1204 was bankrupt by the 1230s, and its emperor Baldwin II was pledging his most valuable assets to Venetian creditors. Among them was a relic venerated as the Crown of Thorns. Louis IX redeemed the pledge in 1239 and had the relic brought to France, walking the last stage barefoot in a plain tunic to receive it outside Sens. Further purchases followed, including a fragment venerated as the True Cross and other objects of the Passion, and the total outlay ran to a sum several times the cost of the chapel he then built to house them.

The Sainte-Chapelle, consecrated in 1248, is not a church of the usual kind. It sits inside the royal palace on the Ile de la Cite, is entered through the king's own precinct, and its upper chapel is walled almost entirely in glass, more than a thousand scenes of stained glass carried on stone mullions so slender that the structure looks impossible. The reliquary shrine stood raised at the east end. The building is an argument as much as a container: it places the relics of Christ's Passion in the keeping of the French crown, and by implication makes Paris a new Jerusalem and the king their guardian.

The acquisition also has a political reading that historians take seriously without treating the devotion as insincere. Louis was a genuinely ascetic man by every contemporary account, who wore a hair shirt, fed beggars at his own table and washed the feet of the poor. He was also assembling for the French monarchy a sacred standing that no other Western dynasty could match, and the Sainte-Chapelle, built by a king who was later canonized, is where those two things are hardest to separate.

Louis IX took the cross after recovering from a severe illness in 1244 and sailed four years later on what is counted the seventh crusade. The expedition took Damietta in Egypt, then broke apart at Mansurah in 1250, where the king was captured with much of his army and ransomed at enormous cost. He did not go home. He spent four more years in the crusader states, fortifying Acre, Caesarea and Jaffa and negotiating with the Mongols, and returned to France only when his mother's death forced it. In 1270 he sailed again, to Tunis, where dysentery killed him and much of his army within weeks of landing. His companion Jean de Joinville, who had refused to go on the second crusade, wrote the memoir that is the closest thing we have to a portrait of him from life.

The canonization came in 1297, pressed by his grandson Philip IV and granted by Boniface VIII in a period when the two were otherwise in bitter conflict. The case rested on his personal austerity, his justice, his hospital foundations including the Quinze-Vingts for the blind, and his death on crusade, which was treated as a martyrdom in intent.

The record also contains this. In 1240 a disputation was staged in Paris over accusations that the Talmud blasphemed Christ, with a converted Jew as prosecutor and Rabbi Yehiel of Paris for the defence. The outcome was a condemnation, and in 1242 wagonloads of Talmudic manuscripts were burned in the Place de Greve, a loss to Jewish learning in northern France from which it did not recover. In 1269 Louis ordered Jews in his kingdom to wear a distinguishing badge. He is recorded as saying that a layman hearing the faith insulted should answer with a sword rather than with argument.