Commentary Par XV 137-138

Cacciaguida's wife came, he says, from the valley of the Po (over the years, Ferrara remains perhaps the favorite location among the discussants, but, since there is a lot at stake [as, for some Americans, there is with regard to George Washington's dining and sleeping habits], the debate goes on).  It was from her, he continues, that Dante got his surname, Alaghieri or Alighieri.  Since one of her and Cacciaguida's sons was named Alighiero, it seems more than likely that he was named for his mother.