Daughter of Louis VIII and of his wife, Blanche of Castille, born in March, 1225; died at Longchamp, 23 February, 1270. St. Louis IX, King of France (1226-70), was her brother. When still a child at court, Isabel, or Elizabeth, showed an extraordinary devotion to exercises of piety, modesty, and other virtues. By Bull of 26 May, 1254, Innocent IV allowed her to retain some Franciscan fathers as her special confessors. She was even more devoted to the Franciscan Order than her royal brother. She not only broke off her engagement with a count, but moreover refused the hand of Conrad, son of the German Emperor Frederick II, although pressed to accept him by everyone, even by Pope Innocent IV, who however did not hesitate subsequently (1254) to praise her fixed determination to remain a virgin. As Isabel wished to found a convent of the Order of St. Clare, Louis IX began in 1255 to acquire the necessary land in the Forest of Rouvray, not far from the Seine and in the neighbourhood of Paris. On 10 June, 1256, the first stone of the convent church was laid. The building appears to have been completed about the beginning of 1259, because Alexander IV gave his sanction on 2 February, 1259, to the new rule which Isabel had had compiled by the Franciscan Mansuetus on the basis of the Rule of the Order of St. Clare. These rules were drawn up solely for this convent, which was named the Monastery of the Humility of the Blessed Virgin (Monasterium Humilitatis B. Mariæ Virginis). The sisters were called in the rule the "Sorores Ordinis humilium ancillarum Beatissimf Marif Virginis". The fast was not so strict as in the Rule of St. Clare; the community was allowed to hold property, and the sisters were subject to the Minorites. The first sisters came from the convent of the Poor Clares at Reims. Isabel herself never entered the cloister, but from 1260 (or 1263) she followed the rules in her own home near by. Isabel was not altogether satisfied with the first rule drawn up, and therefore submitted through the agency of her brother Louis IX, who had also secured the confirmation of the first rule, a revised rule to Urban IV. Urban approved this new constitution on 27 July, 1263.
The difference between the two rules consisted for the most part in outward observances and minor alterations. This new rule was also adopted by other French and Italian convents of the Order of St. Clare, but one can by no means say that a distinct congregation was formed on the basis Isabella's rule. In the new rule Urban IV gives the nuns of Longchamp the official title of "Sorores Minores inclusæ, which was doubtlessly intended to emphasize closer union with the Order of Friars Minor. After a life of mortification and virtue, Isabella died in her house at Longchamp on 23 February, 1270, and was buried in the convent church. After nine days her body was exhumed, when it showed no signs of decay, and many miracles were wrought at her grave. In 1521 Leo X allowed the Abbey of Longchamp to celebrate her feast with a special Office. On 4 June, 1637, a second exhumation took place. On 25 January, 1688, the nuns obtained permission to celebrate her feast with an octave, and in 1696 the celebration of the feast on 31 August was permitted to the whole Franciscan Order. They now keep it on 1 September. The history of the Abbey of Longchamp had many vicissitudes. The Revolution closed it, and in 1794 the empty and dilapidated building was offered for sale, but as no one wished to purchase it, it was destroyed. In 1857 the walls were pulled down except one tower, and the grounds were added to the Bois de Boulogne.
AGNES D'HARCOURT, third Prioress of Longchamp (1263-70), wrote the saint's life, Vie de Madame Isabelle, which may be found in the Archives Nationales L. 1021 MSS. (Paris). A Latin translation of this book is given in Acta SS., VII, Aug., 798-808; cf. ibid., 787-98. See also ROULLIARD, La sainte mère, ou vie de Madame Saincte Isabel (Paris, 1619); ANDRÉ, Histoire de Ste Isabelle (Carpentras, 1885); DANIÉLO, Vie de Madame Ste Isabelle (Paris, 1840); BERGUIN, La Bienheureuse Isabelle de France (Grenoble, 1899); DUCHESNE, Histoire de l'abbaye royale de Longchamp, 1255-1789 (2nd ed., Paris, 1904); SBARA-LEA, Bull. Franc., III (Rome, 1765), 64-9; II (1761). 477-86.