Studying early modern medico-legal testimonies can enrich our understanding of witnessing, the focus of much research in the history of science. Expert testimonies were well established in the Roman Canon law, but the sphere of competence of expert witnesses—one of the grounds on which seventeenth-century physicians claimed social and intellectual authority—troubled contemporary jurists. By reconstructing these debates in Counter Reformation Rome, and by placing in them the testimonies given by Paolo Zacchia, one of the founding fathers of legal medicine, this (...) article discusses the epistemological and social issues surrounding the definition of expertise about the body in court. It shows how a high-ranking expert witness would define his competence versus the legal authority on the one hand, and versus lay and lower-status expert witnesses on the other. But it also explores the interactions between specific legal constraints, for example about eye witnessing, and the ways in which different kinds of witnesses would use the body as a source of evidence for testimony. While engaging with medico-legal issues including the ambiguous signs of childbirth and the visibility of pain, the article examines their meanings within Counter Reformation social controversies, including control over sexuality, imposition of discipline and the social status of physicians.Author Keywords: Legal medicine; Seventeenth-century Rome; Expert witnesses; Testimony; Body; Zacchia. (shrink)