Mediaeval encyclopaedias described nonhuman animals in terms of their corporeality and cosmic significance by combining zoological and theological knowledge. Such descriptions were therefore prescriptions of normative parameters for how animals were supposed to function within Christian society, rather than objective observations. As mediaeval conceptualisations of species were highly malleable, particular animals that shared no biological relation could be considered kin, and animals who behaved against their prescribed nature could become a different animal altogether. This paper investigates how several species were implicated in the mediaeval invention of what it meant to be (like) a pig. My counter-hegemonic reading of the Livre des propriétés des choses, a fifteenth-century French encyclopaedia, draws attention to how late mediaeval Christian scripts of porcinity simultaneously defined the nonhumanity of pigs and of ‘other’ humans. These render the idea of the pig inseparable from what it meant to be human. I contend that the Livre des propriétés des choses employs discourses of porcinity to self-define and -stabilise particular notions of human identity by debasing and othering human and nonhuman animals with seemingly porcine traits. Additionally, I underline how such fabrications of humanity are often mired in practices that devaluate and harm real animals, including other humans. Mediaeval studies need to further address the crucial roles of animal suffering in human history. This way, historians can add valuable insights to present debates about anthropocentrism and its devastating socio-ecological consequences.