[HarryT]

From Wikipedia:

Dante wrote the Comedy in a new language he called "Italian", based on the regional dialect of Tuscany, with some elements of Latin and of the other regional dialects. By creating a poem of epic structure and philosophic purpose, he established that the Italian language was suitable for the highest sort of expression. In French, Italian is nicknamed la langue de Dante. Publishing in the vernacular language marked Dante as one of the first (among others such as Geoffrey Chaucer and Giovanni Boccaccio) to break from standards of publishing in only Latin (the languages of liturgy, history, and scholarship in general). This break allowed more literature to be published for a wider audience - setting the stage for greater levels of literacy in the future.