Commentary Purg X 112-120

This passage has caused much discussion but in fact is not as difficult as it has been made to seem. Virgil's entire purpose in it is to get Dante to understand that what he is looking at is human and not merely a procession of mobile rocks. He admits that he, too, at first found it difficult to grasp this fact, but eventually discerned that there were beings moving beneath the rocks. A single gesture makes this clear: they are beating their breasts. And this is a gesture that accords with the penitential feelings of the penitent prideful, as Moore (Moor.1896.1), p. 49, clearly pointed out, citing Luke (18:13), where the publican beats his breast in humility -- as Dante himself, we may remember, had just done before the keeper of the gate ([Purg IX 111]).