Along with their work as translators and adaptors of plays, the humanists also investigated classical theories of dramatic structure, plot, and characterization. Horace was translated in the 1540s, but had been available throughout the Middle Ages. A complete version of Aristotle's "Poetics" appeared later (first in 1570 in an Italian version), but his ideas had circulated (in an extremely truncated form) as early as the 13th century in Hermann the German's Latin translation of Averroes' Arabic gloss, and other translations of the "Poetics" had appeared in the first half of the 16th century; also of importance were the commentaries on Aristotle's poetics by Julius Caesar Scaliger which appeared in the 1560s. The fourth century grammarians Diomedes and Aelius Donatus were also a source of classical theory. The 16th-century Italians played a central role in the publishing and interpretation of classical dramatic theory, and their works had a major effect on French theater. Lodovico Castelvetro's Aristote-based "Art of Poetry" (1570) was one of the first enunciations of the three unities; this work would inform Jean de la Taille's "Art de la tragedie" (1572). Italian theater (like the tragedy of Gian Giorgio Trissino) and debates on decorum (like those provoked by Sperone Speroni's play "Canace" and Giovanni Battista Giraldi's play "Orbecche") would also influence the French tradition.