Ten thousand years ago, when smallpox first emerged, humankind could do little more than pray to the gods for succor. Later known as variola, the virus that caused the disease first attacked the linings of the nose or throat, spreading throughout the body until a characteristic rash followed by virus-filled blisters developed on the skin. Over the course of recorded history, the “speckled monster” killed up to a third of the people it infected. During the 20th century alone, it felled more than 300 million men, women and children.