The late ancient body is a historiographical problem. In the combined lights of feminist, Foucaultian, and post-Foucaultian methodologies, much recent scholarship on bodies in late antiquity has focused on bodies as sites on which power relations are enacted and as discourses through which ideologies are materialized. Contemporary concern with definitions and representations of the posthuman, however—for example, in medical technologies that expand the capacities of particular human bodies, in speculative pursuit of the limits of avatars, or in the technological pursuit of artificial intelligence or artificial life—seem both to underline the fundamental lability of the body, and to require a broadening of scholarly focus beyond the traditional visible boundaries of the human organism. At the same time, scholarship on the posthuman emphasizes contemporaneity and futurity to an extent that may seem to preclude engagement with the premodern. I would like to suggest here that doubt about the boundaries of human embodiment is a useful lens through which to reconsider some very traditional questions in the history of Christianity, and that we may begin to think of bodies in Christian premodernity in terms of what we might call their pre-humanity, that is, as fundamentally open to extension, transformation, and multiple instantiation. The figure on whom I focus is Ambrose, the fourth-century bishop of Milan, who, I argue, defined his own body in such a way that he was able to instantiate physically in dozens of living human bodies, at least two dead human bodies, thousands of angelic bodies, and four church buildings. Ambrose's dynamic conception of his episcopal body was formed within a complex political and theological situation, so questions concerning the political ideology of bodies remain very much at issue. I add to these questions a concern for premodern uncertainty about how to recognize a body, both when it is visible and, perhaps more importantly, when it is not.