Dante is just gazing with admiration at three stars (symbols of Faith, Hope, and Charity), when Sordello suddenly points out the serpent, who is no sooner descried by the angels than they swoop down and put him to flight. "I saw not, nor can tell, How those celestial falcons from their seat Moved, but in motion each one well descried. Hearing the air cut by their verdant plumes, The serpent fled; and, to their stations, back The angels up return'd with equal flight." _Canto IX._ Dante falls asleep in this valley, but, just as the first gleams of light appear, he is favored by a vision, wherein--like Ganymede--he is borne by a golden-feathered eagle into a glowing fire where both are consumed. Wakening with a start from this disquieting dream, Dante finds himself in a different spot, with no companion save Virgil, and notes the sun is at least two hours high. Virgil now assures him that, thanks to Santa Lucia (type of God's grace), he has in sleep been conveyed to the very entrance of Purgatory. Gazing at the high cliffs which encircle the mountain, Dante now perceives a deep cleft, through which he and Virgil arrive at a vast portal (the gate of penitence), to which three huge steps of varying color and size afford access. At the top of these steps, on a diamond threshold, sits the Angel of Absolution with his flashing sword. Challenged by this warder, Virgil explains that they have been guided hither by Santa Lucia, at whose name the angel bids them draw near. Up a polished step of white marble (which typifies sincerity), a dark step of cracked stone (symbol of contrition), and one of red porphyry (emblem of self-sacrifice), Dante arrives at the angel's feet and humbly begs him to unbar the door. In reply the angel inscribes upon the poet's brow, by means of his sword, seven _P's_, to represent the seven deadly sins (in Italian _peccata_), of which mortals must be purged ere they can enter Paradise. After bidding Dante have these signs properly effaced, the angel draws from beneath his ash-hued mantle the golden key of authority and the silver key of discernment, stating that when St. Peter entrusted them to his keeping he bade him err "rather in opening than in keeping fast." Then, the gate open, the angel bids them enter, adding the solemn warning "he forth again departs who looks behind."