De Regimine Principum (On the Rule of Princes)
De regimine principum
Rex enim non debet esse servus passionum sed dominus earum, et debet habere passiones sub ratione bene ordinatas.
Our renderingA king ought not to be a slave to his passions but their master, and his passions should be rightly ordered under reason.
What it is
Giles of Rome's De regimine principum is the most widely copied Mirror for Princes of the medieval period, composed c. 1277–1280 and dedicated to the young Philip, later Philip IV of France, whose father Philip III had entrusted Giles with the heir's education. The work divides into three books: the individual virtuous conduct of a ruler; domestic governance; and political governance in peace and war. It became a required text in arts faculties at Paris, Oxford, and other European universities, and was translated almost immediately into French by Henri de Gauchy, and later into Italian, Middle English by John Trevisa, and Hebrew — evidence of its near-universal adoption as the standard formation text for heirs to European thrones, with over 300 Latin manuscripts surviving.
Why it still matters
Though a political formation text rather than a prayer book, the first book's chapters on temperance, prudence, and the governance of anger remain practically applicable for any Christian in public life; modern English translations published by Cambridge University Press make the text accessible.
Kept alongside
On the Rule of Princes (De regimine principum)
De regimine principum
Written by the Augustinian friar Giles of Rome at the request of Philip III of France and dedicated to the future Philip IV ('the Fair'), this is among the most widely copied non-religious medieval texts, surviving in approximately 350 manuscripts across Latin, French, Italian, Hebrew, and other vernacular versions. Giles synthesized Aristotle's newly available Politics with Thomistic Christian theology to produce a comprehensive account of personal, domestic, and political virtue for the Christian ruler. Its three books—governing the self, the household, and the realm—made it a standard royal curriculum text across Capetian France, Plantagenet England, and the Iberian kingdoms; Richard III of England owned a copy (Lambeth Palace Library, Sion College MS L40.2/L26).
On the Education of Noble Children (De eruditione filiorum nobilium)
De eruditione filiorum nobilium
Commissioned directly by Queen Margaret of Provence for the royal children of Louis IX's court, this treatise was composed between 1247 and 1249 for the young Prince Louis and Princess Isabelle. Vincent, a Dominican friar at the royal abbey of Royaumont, designed it as the first medieval educational manual to address the formation of both boys and girls in a single systematic treatment. Grounding pedagogy in Ecclesiasticus 7:25–26, it treats Christian moral formation—virtue, scripture reading, and ordered prayer habits—as the foundation of all noble education. While Theobald V of Champagne encouraged Vincent's broader instructional opus, the specific commission for this treatise came from Queen Margaret.
On the Moral Instruction of a Prince (De morali principis institutione)
De morali principis institutione
Composed at the express request of King Louis IX of France in the final years of Vincent's life, this treatise is the first volume of a planned but never-completed 'Opus universale de statu principis.' It addresses the legitimacy and exercise of political power, the vices endemic to courts, and the prudence a prince must bring to governance. Nine manuscripts and one incunabulum survive, attesting limited but sustained scholarly circulation. Louis IX's personal patronage—he funded the scriptorium at Royaumont—makes the royal connection direct and documented.