Michael Ward argues convincingly that medieval cosmology, a subject which fascinated Lewis throughout his life, provides the imaginative key to the seven novels. Drawing on the whole range of Lewis's writings (including previously unpublished drafts of the Chronicles), Ward shows that the Narnia stories were designed to express the characteristics of the seven medieval planets-the Sun, the Moon, Mars, Mercury, Venus, Jupiter and Saturn-planets which Lewis
described as "spiritual symbols of permanent value" and "especially worthwhile in our own generation." Using these seven symbols, Lewis secretly constructed the Chronicles so that the story-line in each book, countless points of ornamental detail, and, most important, the portrayal of the Christ-figure of
Aslan, all serve to communicate the governing planetary personality.