• From the Incarnation of Christ down to his own birth, the planet Mars had returned to the sign of the Lion five hundred and eighty times, or made this number of revolutions in its orbit. Brunetto Latini, Dante’s schoolmaster, Tresor , I Ch. CXI , says, that Mars “goes through all the signs in II years and I month and XXX 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.