Probatio diabolica – On the Origins of the Term
Probatio diabolica – On the Origins of the Term

Summary/Abstract: The article begins by outlining the problem of the burden of proof in Roman property disputes, focusing on rei vindicatio and the actio Publiciana in rem. According to established Roman doctrine, a plaintiff seeking to recover property through rei vindicatio bore the burden of proving ownership. In cases of derivative acquisition, this meant showing an unbroken and legitimate sequence of transfers, confirming that each previous holder had lawfully acquired the property from his predecessor, all the way back to the original acquisition. This evidentiary burden, though ostensibly alleviated by the actio Publiciana, came to be characterised as probatio diabolica. Contrary to the dominant view that locates the term’s origins in Accursius’ Glossa Ordinaria, the article proposes that its true source lies in the late medieval literary genre of “Satanic lawsuits.” This literature is rooted in the patristic ransom theory of atonement, which held that Christ redeemed humanity from the dominion of the devil through his death. The paper follows this narrative from early portrayals of the devil, as plaintiff, asserting dominion over humankind – cast as defendant and represented by the Virgin Mary – to the more procedurally plausible and juridically elaborate accounts of the processus Belial, in which Satan prosecutes Christ over the possession of humankind, now transformed from defendant into the very object of the dispute. Both strands of this tradition turn upon the dualism of possessorium and petitorium, while the theologically scripted “trials,” in which Satan was destined to lose, supplied the metaphorical groundwork for what later came to be understood as diabolical proof.

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