[18] Then, having received in his own mind, as on a waxen tablet, the form of each building, he carries in his heart the image of a city, perceptible as yet only by the intellect, the images of which he stirs up in memory which is innate in him, and, still further, engraving them in his mind like a good workman, keeping his eyes fixed on his model, he begins to raise the city of stones and wood, making the corporeal substances to resemble each of the incorporeal ideas.