Commentary Inf III 82-83

Charon, named twice by Virgil (Aen. VI.299, VI.326), is the 'star' of the moving scene of the crowding dead, buried and unburied, who flock toward the Acheron in the Aeneid (VI.295-330). He is referred to as portitor (VI.298), literally the guardian of the port, but his function in Virgil is to ferry the dead across Acheron. Dante revisits this scene for several details, including the first image in his celebrated simile (vv. 112-113) that awaits us. Unlike the crowds in Virgil, of whom Charon has to separate the buried from the unburied, condemned to wait one hundred years before they can be ferried to the locus their afterlives, in Dante's treatment (vv. 100-111) the souls, having already undergone the Last Judgment (and this scene is probably meant to remind us of that one), are loath to cross to their final resting place, and Charon has to urge them onward physically.