The history of the Italian language is quite complex but the modern standard of the language was largely shaped by relatively recent events. The earliest surviving texts which can definitely be called Italian (as opposed to its predecessor Vulgar Latin) are legal formulae from the region of Benevento dating from 960-963.
During the 14th century the Tuscan dialect began to predominate, because of the central position of Tuscany in Italy, and because of the aggressive commerce of its most important city, Florence. In fact, Florentine culture produced the three literary artists who best summarized Italian thought and feeling of the late Middle Ages and early Renaissance: Petrarca, Boccaccio and, specially, Dante Alighieri. Dante was the one who mixed southern Italian languages, especially Sicilian, with his native Tuscan ("supposed" to be derived from Etruscan and Oscan) in his epic poems known collectively as the Commedia, to which Giovanni Boccaccio later affixed the title Divina.
The "question of the language", an attempt to establish linguistic norms and codify the language, engrossed writers of all persuasions. Grammarians during the 15th and the 16th centuries attempted to confer upon the pronunciation, syntax, and vocabulary of 14th-century Tuscan the status of a central and classical Italian speech. Eventually this classicism, which might have made Italian another dead language, was widened to include the organic changes inevitable in a living tongue.
In the dictionaries and publications of the Accademia della Crusca, founded in 1583, which was accepted by Italians as authoritative in Italian linguistic matters, compromises between classical purism and living Tuscan usage were successfully effected. The most important literary event of the 16th century did not actually take place in Florence. In 1525 the Venetian Pietro Bembo (1470-1547) set out his proposals (Prose della volgar lingua - 1525) for a standardized language and style: Petrarca and Boccaccio were his models and thus became the modern classics. Therefore, the language of Italian literature is modeled on that spoken in Florence in the 15th century.
In fact, the first edition of an official Italian vocabulary, published in 1612 by the Accademia della Crusca, was built on the basis of the following Florentine works: “Divina Commedia” by Dante, “Decameron” by Bocaccio and “Canzionere” by Petrarca. Today, Toscano is still considered the "cleanest" of all Italian dialects as it is the most similar to the original or classical Latin.
However, It was not until the 19th century that the language spoken by educated Tuscans spread to become the language of a new nation. The unification of Italy in 1861 had a profound impact not only on the political scene but also resulted in a significant social, economical, and cultural transformation. With mandatory schooling, the literacy rate increased, and many speakers abandoned their native dialect in favor of the national language.