The idol, in medieval Christian analysis, is a paradoxical object; it may be conceived of either as mere dumb matter, or as the housing of a living demon. It is paradoxical, too, in contemporary theories of materiality; the idol is a paradigm of the material thing invested with agency, but how then does it find space to develop the excess that makes it an agent, not a mere machine? This article argues that Christian narratives of the origin of idolatry explore this very question. St. Augustine drew together different strands of Old Testament denunciations of idolatry to argue that demons were attracted to the material images built by pagans. The idol is animated by the devotional pagan gaze, but exerts power by latency: at some times it will display liveliness to its worshippers, at others it will remain indifferent. Though the theory is worked out in most detail in regard to idols, Christian images, too, work through the power of latency, and may seduce and trap unwary viewers by apparent inertia.