What first prompted prehistoric man, sheltering in the shadows of deep caves, to call upon the realm of the spirits? And why has belief thrived ever since, leading us to invent heaven and hell, sin and redemption, and above all, gods? Religion reflects our deepest hopes and fears; whether you are a believer or, like Matthew Kneale, a non-believer who admires mankind's capacity to create and to imagine, it has shaped our world. And as our dreams and nightmares have changed over the millennia, so have our beliefs - from shamans to Aztec priests, from Buddhists to Christians: the gods we created have evolved with us. Belief is humanity's most epic invention. It has always been our closest companion and greatest consolation. To understand it is to better understand ourselves.