[2] He may be the William of Chartres described as a cleric and scholar at Vercelli who stood as surety for some Frenchmen studying in Italy in 1231.
[3][4] In March 1251, Louis provided William's two sisters and their eldest sons with an income from rents.
In 1254–1255, acting as a royal agent, he purchased properties on the left bank of the Seine for the Sorbonne.
The three carried four letters from Philip dated 12 September 1270 informing the ecclesiastical and lay magnates of the kingdom of Louis's death and confirming Matthew of Vendôme and Simon of Nesle in the regency.
[9] They travelled by way of Sicily and Italy, crossing the Alps and arriving at Paris by early October.
[12] The last record of William is an undated letter he wrote to his brother-in-law, Gilles de la Chaussée, probably in 1277.
[14] On the Life and Deeds of Louis, King of the Franks of Famous Memory, and on the Miracles That Declare His Sanctity, William's Latin biography of Louis IX, is preserved alongside Geoffrey of Beaulieu's in a single manuscript, BnF, MS lat.
He enumerated four areas where he intended to complete Geoffrey's biography: "the good days of [Louis's] rule", his imprisonment, his death and the miracles that had occurred at his tomb and through his intercession.
[19] In recounting the justness of Louis's administration—e.g., his suppression of private warfare and trial by battle—On the Life and Deeds reads at times like a mirror of princes.
[5] Paragraphs 1–3 of contain metaphors comparing Louis to the sun among stars and the Biblical king Josiah.
Paragraph 4 is a description of Louis's institution of an annual procession of the relic of the crown of thorns at Sainte-Chapelle.
William breaks with his declared themes at paragraph 11, where he tells how Louis had predicted that he would become a Dominican, and paragraphs 28–36, which describe Louis's various acts of religious devotion: footwashing, fasting, almsgiving, caring for lepers, building hospitals for the poor and endowing friaries and churches.
[23] William presents all the miracles as properly authenticated, usually dated, and apparently collected many of the accounts himself.
[24] All seventeen recorded by William were later included in the Beatus Ludovicus, which assured them a wider audience than On the Life and Deeds received.