Gui was one of the most prolific Latin authors of the
Late Middle Ages, although he rarely wrote original works, preferring instead to compile and arrange existing texts, anecdotes, and records. He ordered the construction of a library at Limoges to accommodate over one hundred volumes; this was completed in 1306 and represented "one of the earliest efforts in the West to build a room devoted especially to the preservation of books". The Dominican monastery at Limoges had been a "centre for historical study" for over a century, and Gui compiled numerous works of history (referred to by Gui as 'chronography'). These included the
Flores chronicorum, a
universal history from the birth of Christ to Gui's death in 1331, and various
local histories, including accounts of the saints of
Limousin (
Traité sur les saints du Limousin), the abbey of Limoges (''Traité sur l'histoire de l'abbaye de St. Augustin de Limoges
), the priors of Grandmont (Chronique des prieurs de Grandmont'') and L'Artige (''Chronique des prieurs de l'Artige
), and the bishops of Toulouse (Chronique des évêques de Toulouse
) and Limoges (Catalogue des Évêques de Limoges
). Additionally, he completed and significantly expanded the De Quator in quibus Deus Praedicatorum ordinem insignivit,'' a historical treatise on the Dominican Order begun in the 1270s by Stephen of Salanhac, and uncompleted at the time of the latter's death in 1291. This was largely completed by 1311, although Gui continued to make minor additions until his death. Gui also compiled the
Chronique des rois de France in 1313
, an illustrated
genealogy of the kings of France. This included the
Arbor genealogiae regum francorum, one of the earliest known examples of a
family tree, which was widely reproduced. He also contributed his literary energies to the campaign for the
canonisation of
Thomas Aquinas, producing the
hagiography Vita Sancti Thomae Aquinatis (based largely on extant works by William of Tocco) in 1318 and a catalogue of his works in 1320. He probably attended the canonisation ceremony in Avignon in July 1323. However, Gui's best-known works are those related to his inquisitorial career:
Liber sententiarum, a comprehensive register of the sentences he delivered, and
Practica inquisitionis heretice pravitatis, a comprehensive inquisitor's manual. Inquisitors had no standardised or formal training, although they were often educated in theology or law, and practical guides to inquisitorial activities emerged as a distinct literary genre in the late twelfth century. Gui's manual consisted of five books: the first three were
formularies, providing templates to be used to deliver sentences during 'general sermons', and the fourth reproduced documents outlining and confirming the powers of the inquisitor (such as papal and conciliar legislation, and royal decrees). The fifth and most famous book provided descriptions of the beliefs and practices of heretics such as
Cathars (referred to as 'modern
Manicheans'),
Waldensians,
Pseudo-Apostles,
Beguines, and relapsed Jews, in addition to guidance for inquisitors on the best methods of interrogation for each group (including advocating torture if necessary). This was the first inquisitor's manual to refer specifically to penalties for relapsed Jews. The exact date of the text's composition is unclear, but Janet Shirley suggests a completion date of early 1324 at the latest. The manual was based on Gui's practical experience, but it also relied heavily on the writings of others for subjects in which he had little experience; for example, his description of the Waldensians includes passages lifted directly from
Stephen of Bourbon's
Tractatus de diversis materiis predicabilibus and
David of Augsburg's
De inquisitione hereticorum. Gui's text was one of the most widely copied and read inquisitorial manuals during the medieval period, superseded only by the Catalan inquisitor
Nicholas Eymerich's fourteenth-century
Directorium Inquisitorum, and heavily influenced later inquisitorial practice. Six manuscripts of the work survive, located in the archives of Toulouse, the
Vatican Library, the
British Museum, and the
Bibliothèque Nationale in
Paris. The first
printed edition was published in 1886, when the text was translated to French by the
Bishop of Beauvais, Marie-Jean-Celestin Douais. File:Bernard Gui BNF lat4975.jpg|Illustrations from a copy of Gui's
Arbor genealogiae regum francorum produced in the 1330s, showing the
Carolingian kings
Lothair and
Louis V File:Gui, Bernard – Practica officii inquisitionis heretice pravitatis, 14th-century – BEIC 9975680.jpg|
Practica officii inquisitionis heretice pravitatis, manuscript, 14th century. Toulouse, Bibliothèque d'Etude et du Patrimoine, Fonds Manuscrits, Ms 388. ==Popular culture==