The ‘insider-outsider problem’ has had little impact on the study of religion in pre-Christian Rome. Classicists generally assume that the modern idea of sacrifice as the ritual killing of an animal applies to the Roman context. This study argues, however, that the apparent continuity is illusory in some important ways and that we have lost sight of some fine distinctions that the Romans made among the rituals they performed. Sacrificium included vegetal and inedible offerings, and it was not the only Roman ritual that had living victims. Roman sacrificium is both less and more than the typical etic notion of sacrifice.