He was twelve years old when he became king, although his right of succession was at first disputed. However, his formidable mother, Blanche of Castile, had twice as queen-regent to take up arms to defeat rebellious nobles. In 1234 he married Marguerite de Provence and in 1236 he took over the reigns of government. However, Blanche of Castile was reluctant to let power go and because of this, Louis IX treated her with extravagant respect. She was also jealous of Marguerite de Provence and in the first years of married life tried to keep them apart. Nevertheless Louis IX proved to be the stronger character and, even though he put up with his mother's caprices, he had his way in essential matters.

Louis IX and Marguerite became the parents of nine children. Marguerite also wanted to interfere in politics but in these matters Louis IX kept her at arm's length, yet took her with him on his first crusade. Louis IX was a very handsome man, tall and elegant, and his people noted his mild and kind look. Early in the morning he would leave the palace to distribute money to the poor as anonymously as possible. At midnight he would hear Mass for the dead. On Fridays he neither indulged any frivolity nor, in memory of the crown of thorns, wore a hat; and like most monarchs he washed the feet of the poor. His dress was almost like a monk's and one day his wife reproached him for not wearing more regal dress. He then maintained that each spouse had to please the other and so he would dress more richly to please her, but then she would have to please him by disposing of her rich dresses. Always self-confident, he loved to sing and jest with his companions, and was so strong of will that most men feared him. In 1248 he went on crusade accompanied by his wife and two brothers. In 1249 he took Damietta on the mouth of the Nile and should have continued on to take Cairo; but instead he dallied to pray while his crusaders enjoyed the fleshpots of the Near East. The Sultan was then able to bring reinforcements and, when they marched to Cairo, they were cut off from Damietta and no food could reach the French. Meanwhile Louis and his army suffered from dysentery and finally had to surrender to the Muslims, although in Damietta the queen and her force still held out. Louis IX was led around in triumph but, when the Egyptians felt embarrassed at having so many prisoners, at night in groups of three or four hundred they were taken to the Nile where, after their heads were cut off, they were thrown into the river. Louis IX and those nobles still alive were ransomed and returned to the queen in Damietta, after which Damietta had to be returned to the Muslims. After this disaster he stayed two more years in Palestine; but he remained unsuccessful as no support was offered as Europe had lost the taste for crusades. However, back in France he won two victories over the English at Taillebourg and Saintes. But to the surprise of Europe, the victorious king gave back three provinces of France to Henry III, stating that there should be peace and amity between Christians. However, he demanded that the English king should pay him homage and abandon all claims to the throne of France.

In the summer of 1270 Louis IX set out for another crusade. As he believed the Bey of Tunis intended to become a Christian, he thought it would be a friendly visit. More probably he was induced to go to Tunis by his brother Charles of Anjou, King of Sicily, who wanted to stop the pirates using Tunis as their base. Some people regarded the whole expedition as a sin as the kingdom was at peace with all its neighbours, including Tunis. Another reason was Louis IX's physical condition; he could not bear to be carried or to ride on horseback. He landed at Carthage in mid-summer when the pest was raging in Tunisia. After a victorious fight before the walls of Tunis, the French army was immobilized by the disease and, on 25 August 1270, the king died of it. 

Source: Leo van de Pas