Commentary Inf XV 61-78

Brunetto, like Farinata ([Inf X 79-81]), prophesies Dante's exile. His sense of the history of Florence (perhaps reflecting his own treatment of this subject in the first book of his Tresor) puts forward the legend that Florence was populated by the Romans after they destroyed neighboring Fiesole in order to put an end to Catiline's conspiracy. Unfortunately, their descendants, the Florentine nobility, allowed the surviving Fiesolans to emigrate and mix their base population with the Roman stock. For Dante, all the city's (and his own) troubles stem from this original mistake.