GAIO. - Roman jurist, who lived in the age of the Antonines. Nothing is known of his life; but, based on certain peculiarities in his works, some believe that he was an Easterner.
He is the author of Libri ex Quinto Mucio (a work relating to the ius civile), a commentary on the edict of the urban praetor and the provincial edict, and Twelve Tables (v.). The Libri aureorum or rerum cottidianarum have also been attributed to him, which, however, are very probably a post-classical free paraphrase of G.'s principal work. The latter is represented by the Institutiones, whose almost complete text, discovered in 1816 in the Chapter Library of Verona and supplemented by fortunate subsequent finds, provides an elementary exposition of classical Roman law. The Institutiones are divided into four books, which set forth the matter relating to personae (I), res (things, acquisition of property, successions, obligations: II and III) and actiones (procedure: IV). The most recent critical edition of the Institutiones is that edited by B. Kübler (Leipzig 1935); among the recent Italian editions, mention should be made of the one edited by G. Baviera, in Fontes iuris anteiustiniani (II, Florence 1940, pp. 5-102) and the one edited by V. Arangio-Ruiz and A. Guarino, in Breviarium iuris Romani, Milan 1943, pp. 3-194.