How did the Tuscan dialect become the basis of standard Italian literary language?

The Tuscan dialect, specifically the variety spoken in Florence, became the foundation of standard Italian primarily through the prestige of its 14th-century literary masters and subsequent codification efforts.12

By the end of the 13th century, Tuscan was already emerging as the primary vernacular in a land otherwise dominated by regional dialects and Latin. The preeminence of the dialect was cemented by the works of three foundational writers:3
* Dante Alighieri: His choice of Tuscan for The Divine Comedy established the dialect as a powerful literary medium.3
* Petrarch and Giovanni Boccaccio: Their works became the stylistic benchmarks for the language.32

In 1525, Pietro Bembo published Prose della volgar lingua, which formally advocated for an Italian literary language modeled specifically on the 14th-century Tuscan of Petrarch and Boccaccio. Bembo’s theories eventually triumphed, bolstered by the Accademia della Crusca, which further standardized the language through its 1612 dictionary.2