Paradise Canto XVI: (Fifth Heaven: Sphere of Mars)
Dante takes a short break to bask in his glory.
He turns back to Cacciaguida and shows him a great sign of respect by addressing him with the formal form of you, usually reserved for nobility.
Dante calls Cacciaguida "my father" and says that his nobility has given him the confidence to ask further questions. Dante wants to know who Cacciaguida's ancestors were, when Cacciaguida lived, and who virtuously followed St. John (patron saint of Florence) at the time.
Cacciaguida grows brighter with gladness, then answers in a style of speech sweeter than the harsh modern style. He answers Dante's second question, about the year of his birth, first. Starting from the date of Christ's conception and adding 530 revolutions of Mars (because he resides there) around the Earth, we get the date 1091.
Of Dante's ancestors, Cacciaguida says only they that they were born at the point where the competitors in the annual horse race enter the field.
Cacciaguida then falls silent about the ancestors because, on that subject, "silence—not speech—is more appropriate."
In response to Dante's last question, Cacciaguida says that St. John's followers included one-fifth of the entire Florentine population.
Cacciaguida laments that Florence doesn't have the smaller boundaries today that it did in the beginning. If it did, he says, Florentines might still be virtuous, pure-blooded Florentines. He even goes so far to blame interracial mixing as the root of evil in Florence.
Cacciaguida then names a bunch of families who had illustrious names in good Florence and some families who were starting to go bad. He generally claims that the families and the clergy of the past were honorable people, but that time has seen the clerics become corrupt. Time has had a bad effect on poor Florence.
In fact, back in the glory days, "there was nothing to have caused her (Florence) sorrow." Things were so good that in Florence's emblem—the white lily on a red field—the lily was never stained blood-red by war between Florentine factions, nor were the colors reversed (to a red lily on a white field) by the Guelphs against the Ghibellines.