Commentary Inf XX 97-102

Capping his (to us absurd yet amusing) contradiction of the details of the founding of Mantua published in his own poem, Virgil now gets Dante to swear that he will regard only the current version of that history as truthful, and that he will consider any other version, i.e., the Roman poet's own, as nothing other than a lie. The protagonist dutifully assents. Thus is Virgil made to remove the stain of divination from his poem and from himself. The result is eventually quite different from what the tactic might have been intended to secure, i.e., Virgil's poem is seen precisely as associated with this fault. See Barolini (Baro.1998.1), pp. 283-84.