Today we take the word "icon" to mean "a sign," or we equate it with portraits of Christ and the saints. In The Sensual Icon, Bissera Pentcheva demonstrates how icons originally manifested the presence of the Holy Spirit in matter. Christ was the ideal icon, emerging through the Incarnation; so, too, were the bodies of the stylites (column-saints) penetrated by the divine pneuma (breath or spirit), or the Eucharist, or the Justinianic space of Hagia Sophia filled with the reverberations of chants and the smoke of incense. Iconoclasm (726-843) challenged these...