Definition
An action for double the value of a thing — that is, a civil remedy in which the successful plaintiff recovers twice the amount of the loss or the value of the subject matter in dispute. Rooted in Roman civil law, the actio in duplum was a penal action designed not merely to compensate the injured party but to punish the defendant and deter the underlying wrong. The doubled recovery was the penalty itself, built into the form of the action rather than assessed separately.
The action arose in specific procedural contexts under Roman law, most notably in connection with a defendant who denied liability (infitiatio) when suit was brought. A defendant who contested and lost could be condemned in duplum — double the original claim — as a sanction for the denial. This use of doubled damages as a litigation penalty for unsuccessful denial was a characteristic feature of Roman penal procedure and distinguishes the actio in duplum from a simple compensatory action.
Why It Matters in Research
This is a term of Roman civil law that appears in English legal sources primarily through the influence of Bracton and the early common law writers who drew on civilian learning. Researchers encountering actio in duplum in medieval or early modern sources should understand they are reading a civilian concept being translated — sometimes imperfectly — into a common law context.
The critical research trap is treating actio in duplum as a generic phrase for "double damages" in common law. It is not. In its Roman form, the doubling was procedurally and substantively specific: it attached to particular actions and, in many cases, was triggered by the defendant's denial of liability (infitiatio). When Bracton or later common lawyers invoke the term, they are often using it analogically or illustratively rather than transplanting the Roman procedure intact.
Researchers working in equity or early common law sources may find actio in duplum invoked in discussions of debt, theft, loan actions (particularly the actio de tigno iuncto or similar building-material disputes), and in treatments of the condictio. The Institutes passage cited by Burrill (Inst. 4.6.21, 23) addresses the broader taxonomy of Roman actions and the penal character of duplum recoveries — this is the foundational primary source to consult when tracing how the concept was understood by later civilian-influenced writers.
For corpus researchers: appearances of this term in Law Mind sources will cluster in treatises and digests with civilian orientation. Do not expect to find it in standard common law pleading manuals or procedure texts of the seventeenth century onward, where the term would have little operative purchase.
Historical Dictionary Support
Burrill defines the term concisely and accurately: "an action for the double value of a thing," with citations to Justinian's Institutes (4.6.21, 23) and Bracton (fol. 103a). This is the full extent of coverage in the available historical dictionary sources.
Burrill's entry is functional but compressed. It confirms the Roman-law origin and the Bractonian reception but does not elaborate on the procedural mechanics that make the concept distinctive — specifically, the role of infitiatio in triggering the doubled penalty. Researchers relying only on Burrill's gloss risk treating actio in duplum as equivalent to any doubled-damages remedy, which understates the procedural specificity of the Roman form.
No entry for this term appears in standard common law dictionaries of the English tradition (Termes de la Ley, Cowell's Interpreter, Tomlin's), which reflects the term's status as specialist civilian vocabulary rather than received common law terminology.
Jurisdictional Note
The actio in duplum has no direct operative existence in Anglo-American common law jurisdictions. Its relevance in those systems is historical and scholarly — appearing in treatises, academic commentary on Bracton, and comparative legal history. In jurisdictions that received Roman law more directly (Scots law, South African law, certain civil law systems), analogous doubled-penalty actions have had continuing doctrinal significance.