Dante's Dream of the Eagle and the Gate of Purgatory

Dante falls asleep on the grass and dreams of being snatched up by a golden eagle into the sphere of fire. He awakens to find himself at the Gate of Purgatory, with Virgil explaining that Saint Lucia carried him there while he slept. The gate is approached by three steps: white marble, dark cracked stone, and porphyry. An angel with a naked sword sits on the threshold. Virgil asks the angel to open the gate. The angel inscribes seven P's (for peccata, sins) on Dante's forehead with the point of his sword, then uses two keys—gold and silver—to unlock the gate. He warns that whoever looks back must return. The gate opens with a thunderous sound, and Dante hears the 'Te Deum.' This episode marks the formal entry into Purgatory proper.