Irnerius (GARNERIUS), Italian jurist and founder of the School of Glossators, b. at Bologna about 1050; d. there about 1130. Though he was one of the most famous jurists of the Middle Ages, very little is known concerning his life and works, and it is only during the last twenty years that he has received the attention which his influence on the history and development of medieval jurisprudence demands. He was probably little over twenty years of age when he already taught didactics and rhetoric at Bologna. At the instance of Countess Matilda of Tuscany he began to devote himself to the study of jurisprudence, taking the Justinian code as a guide. Up to his time the study of jurisprudence had been much neglected in the empire, and he had to depend to a great extent on private studies, though it is probable that for a time he frequented a law school in Rome After teaching jurisprudence for a short while in Rome he returned to Bologna, where he founded a new school of jurisprudence in 1084. It appears that some jurisprudence had been taught at Bologna, before Irnerius founded his school, by a certain Pepo and a few others; but the great impulse which juridical studies received at Bologna at this time, and from there began to spread throughout Europe, was entirely due to the school of Irnerius. He introduced the custom of explaining the Roman law by means of glosses, which originally were meager interlinear elucidations of the text. But since the glosses were often too extensive to be inserted between the lines of the text, he began to write them on the margin of the page, thus being the first to introduce the marginal glosses which afterwards came into general use. After the death of Pope Paschal II, he defended the rights of Emperor Henry V in the papal election and upheld the legality of the election of the imperial antipope, Gregory VIII.
Irnerius is the author of numerous juridical works, but most of them have either been lost, or their genuineness is not sufficiently established. His chief work is “Summa Codicis”, which is of a special historical value, because it is the first medieval system of Roman jurisprudence. It was recently edited with a critical introduction by Fitting, “Summa Codicis des Irnerius, mit einer Einleitung” (Berlin, 1894). Another important work generally ascribed to Irnerius, is “Quaestiones de juris subtilitatibus”. It was also edited by Fitting, “Quaestiones de juris subtilitatibus des Irnerius, mit einer Einleitung” (Festschrift zum 200 jahrigem Jubilaum der Universitat Halle-Wittenberg, 1894). The other juridical works and glosses that are ascribed to Irnerius are extant only in fragments, or their authorship is still too uncertain.