The three doors in Lanfranco's original design all carry decorations in which a vine-like plant with leaves and tendrils surrounds the figures of men, monsters and animals. The greenery represents the forest, a metaphor for the world, life and sin (the "selva oscura" mentioned by Dante). In the forest, man encounters monsters and fights wild beasts, just as he has to struggle against evil in his life.

On the main doorway, with imagination and skill that should be savoured image by image, Wiligelmo portrays the drama of human life right up the sides of the doors to the archivolt.