Title of the canonical collection of the five books of the Decretals of Gregory IX compiled under order of Boniface VIII
Liber Sextus Decretalium, the title of the canonical collection compiled under order of Boniface VIII by Guillaume de Mandagot, Bishop of Embrun, Berenger Fredoli, Bishop of Beziers, and Ricardo Petroni, of Siena, vice-chancellor of the pope, by whom it was approved as an authentic and official collection in the Bull "Sacrosanctae" of March 3, 1298. Like the "Decretals of Gregory IX", the "Liber Sextus" comprises five books, subdivided into titles and chapters. It contains in addition eighty-eight rules of law (regulce juris) borrowed from the Roman law, and compiled probably by Dino de' Rossoni, professor of civil law at the University of Bologna. It is an obligatory code of laws, abrogating all previous general laws enacted from the time of the publication of the "Decretals of Gregory IX" till the accession of Boniface VIII (September 5, 1234, to December 24, 1294), with the exception of those that were reserved (reservatoe)—that is to say, maintained in vigour—either by decretals inserted in the "Sextus", declaring that these laws were to remain in force, or by their Incipit being included in the collection. The "Decretals of Gregory IX" were revoked, in so far as they were inconsistent with the new statutes. Although Laurin holds the contrary, we believe that the eighty-eight rules of law are also real ecclesiastical laws, because they form part of the collection as approved by Boniface VIII. The glossators of the "Sextus" were Johannes Andrew, author of the ordinary gloss, to which he made some additions later (Additiones ad apparatum super Sexto); Johannes Monachus (d. 1313), and Guido de Baysio (d. 1313). As to the manner of citing the "Sextus", the revision of its text by the Correctores Romani of 1582, and the best editions, see Corpus Juris Canonici.
This canonical collection was called by Boniface VIII himself the "Liber Sextus", firstly, because it is a continuation of the five books of the "Decretals of Gregory. IX", and secondly, because six is a perfect number. This title will indicate, he says in the Bull of approbation ("Sacrosanctae"), that the complete body of canon law, henceforth collected into six books (i.e. a perfect number of books), will furnish a perfect rule of action and be a safe guide in morals. According to Euclid the number six is perfect, because it is equal to the sum of all its factors (I +2+3=6). According to Boethius, a number is to be compared to an organized body, all the parts of which (factors, quotients, or aliquot parts) represent the members. A perfect number thus denotes a body, the members of which are in perfect harmony with that body. So also in the moral order, the perfect number is the emblem of virtue (virtutis cemulator), and, calling this new compilation the "Liber Sextus", the pope wished to signify the happy effects which this collection of canonical legislation would produce.
A. VAN HOVE