Explanations for this passage have abounded, some of which argue that the passage is either a mere "hermeneutic contrivance", a purposeful tactic on the part of Dante to undermine the reader's sense of Virgil's authority, an allusion to a medieval legend about Virgil, a reworking of medieval concepts about necromancy, a literary parallel to Christ's Harrowing of Hell, simply an echo of Virgil's supposed knowledge of Hell (based on his description of the underworld in the "Aeneid", 6.562–565), or merely a reference to the aforementioned episode from Lucan. Gilson contends that the reference to Erichtho reinforces the fact "that Dante's own journey through Hell is divinely willed," although "this is achieved at the expense of the earlier necromantically inspired journey undertaken by Virgil." Similarly, Rachel Jacoff argues: