Guido de Baysio (born about the middle of the thirteenth century of a noble Ghibelline family; died at Avignon, 10 August 1313) was an Italian canonist.
[1] Called to Avignon in 1304 he retained the dignity of archdeacon, held the office of papal chaplain, and also served in the Apostolic chancery until his death.
[1] Baysio's chief work was Rosarium Decretorum, a commentary on the Decretum of Gratian, which he wrote about the year 1300 and dedicated to his patron Gerhard.
[1][3] During the brief pontificate of Pope Benedict XI (1303–1304) he wrote an accurate and complete, but rather diffuse, commentary on the "Liber sextus".
[4] His stay at Avignon was marked by a Tractatus super haeresi et aliis criminibus in causa Templariorum et D. Bonifacii.