days.” This would make Cacciaguida born long after the crusade in which he died. But Dante, who had perhaps seen the astronomical tables of King Alfonso of Castile, knew more of the matter than his schoolmaster, and was aware that the period of a revolution of Mars is less than two years. Witte, who cites these tables in his notes to this canto, says they give “686 days 22 hours and 24 minutes”; and continues: “Five hundred and eighty such revolutions give then (due regard being had to the leap-years) 1090 years and not quite four months. Cacciaguida, therefore, at the time of the Second Crusade, was in his fifty-seventh year.”

Pietro di Dante (the poet’s son and commentator, and who, as Biagioli, with rather gratuitous harshness, says, was “smaller compared to his father than a point is to the universe”) assumed two years as a revolution of Mars; but as this made Cacciaguida born in 1160, twelve years after his death, he suggested the reading of “three,” instead of “thirty,” in the text, which reading was adopted by the Cruscan Academy, and makes the year of Cacciaguida’s birth 1106.