Commentary Purg XIV 16-18

The protagonist introduces its controlling image to the canto, the river Arno.  Its source is in the Apennines at Mt. Falterona and it then makes its way, as we shall hear, through the Casentino, then the cities of Arezzo, Florence, and Pisa, before it reaches the sea.  Giovanna Ioli (Ioli.1989.1), p. 210, points out that the verb saziare (slake) introduces the theme of hunger to this description of the Arno.  The river seems, in order to satisfy its own appetites, not to extend far enough, despite all the harm its ca. 150 miles (and not Dante's 100) produces.