For over half a century, scholars have labored to show that C. S. Lewis's famed but apparently disorganized Chronicles of Narnia have an underlying symbolic coherence, pointing to such possible unifying themes as the seven sacraments, the seven deadly sins, and the seven books of Spenser's Faerie Queene. None of these explanations has won general acceptance and the structure of Narnia's symbolism has remained a mystery. Michael Ward has finally solved the enigma. In Planet Narnia he demonstrates 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, Ward reveals how the Narnia stories were designed to express the characteristics of the seven medieval planets-Jupiter, Mars, Sol, Luna, Mercury, Venus, and Saturn-planets which Lewis described as "spiritual symbols of permanent value." Using these seven symbols, Lewis secretly constructed the Chronicles so that in each book the plot-line, the ornamental details, and, most important, the portrayal of the Christ-figure of Aslan, all serve to communicate the governing planetary personality. Planet Narnia is a groundbreaking study that will provoke a major revaluation not only of the Chronicles, but of Lewis's whole literary and theological outlook.