Beginning with ancient Atomist and Stoic philosophies, Rubenstein links contemporary models of the multiverse to their forerunners and explores the reasons for their recent appearance. One concerns the so-called fine-tuning of the universe: nature's constants are so delicately calibrated that it seems they have been set just right to allow life to emerge. In their very efforts to sidestep metaphysics, theoretical physicists propose multiverse scenarios that collide with it and even produce counter-theological narratives. Far from invalidating multiverse hypotheses, Rubenstein argues, this interdisciplinary collision actually secures their scientific viability.