Commentary Inf V 20

Commentators customarily note that here Dante builds his line out of two sources: Aeneid VI.126: 'Facilis descensus Averno' (the descent to the underworld is easy [but not the return from there]); Matth. 7:13: 'spatiosa via est, quae ducit ad perditionem' (broad is the way that leads to perdition).