Dante sleeps. In the hour before dawn — the hour when, as ancient belief held, dreams most closely approach the truth — he has a vision. An eagle, golden, with wings outspread, sweeps down and carries him up to the sphere of fire in the sky. He wakes, terrified, to find himself much higher on the mountain than he was, beside Virgil. Virgil explains: while he slept, a lady (later understood to be Lucia, one of Beatrice's three ministering graces) came and carried him to the gate of Purgatory proper. The dream was the experience of the carrying, refracted through sleep into mythological terms — Dante's subconscious rendered it as Ganymede, the beautiful youth snatched up by Jove's eagle to serve the gods. The allegory suggests divine grace operating on the soul even when the soul is passive and unconscious.
They reach the gate. Three steps lead up to it, each one a different material and color: the first of white marble, so polished the pilgrim can see his own reflection (the transparency of self-knowledge, of honest confession); the second of dark, cracked, burnt stone — the color of contrition and broken-heartedness; the third of red porphyry, red as blood pulsing from an artery (the love and resolution that animates penance and satisfaction). Upon the red step sits an angel gatekeeper, clothed in grey, holding a naked sword whose blade blazes so bright Dante cannot look at it. The angel draws two letters "P" on Dante's forehead with the sword — one for each of the seven sins (he will receive seven, one for each terrace; later cantos will mention only "the P's"). He inscribes seven P's (peccata, sins) total on Dante's brow, instructing him to wash them off as he climbs. Then the gate swings open with a thunder like iron and rock — and the sounds of voices singing the Te Deum laudamus, the hymn of praise, rise from within.