Definition
In Roman and civil law, a plagiarius was a person who committed plagium — the crime of stealing, detaining, selling, buying, or otherwise wrongfully appropriating a human being. The term encompasses what modern law recognizes as kidnapping and, in its broader Roman application, a form of enslavement or unlawful confinement. The offense applied to:
1. One who stole or abducted a free person (whether freeborn or a freedman) or another person's slave.
2. One who knowingly kept such a person in chains or confinement.
3. One who sold, gave, or purchased a person so detained or stolen.
The Digest of Justinian (Dig. 48.15.1) is the primary classical source for the definition and scope of the offense. Blackstone references the Roman concept in his treatment of offenses against the person (4 Bl. Comm. 219).
Common Language
Modern common usage (Wiktionary): "Plagiarist" — a person who takes someone else's work, ideas, or expressions and presents them as their own, without attribution.
Historical common usage (Webster's 1913): "Plagiarist" — one who plagiarizes; one who purloins the thoughts or writings of another and passes them off as one's own.
The gap here is significant and historically interesting. The modern English word "plagiarist" and its root "plagiarism" descend directly from plagiarius, but through a striking metaphorical shift. Roman jurists used the term literally — a stealer of persons. Early modern writers borrowed the Latin to describe the theft of literary work, treating an author's words as, in effect, their intellectual children. The legal meaning (kidnapper/man-stealer) and the common meaning (literary thief) share a root but are otherwise entirely distinct. A researcher encountering plagiarius in a Latin legal text should not assume any connection to intellectual property or copyright.
Common Confusion
Plagiarius is sometimes loosely equated with servus fuga (a runaway slave) or confused with terms relating to slavery more generally. The distinction matters: plagiarius identifies the wrongdoer — the person committing the abduction or unlawful detention — not the victim. The offense of plagium is also distinct from simple theft (furtum), being classified among the more serious public crimes (crimina extraordinaria) under Roman law, carrying heavier penalties than ordinary property offenses.
Why It Matters in Research
Researchers working in civil law history, Roman law sources, or comparative criminal law will encounter plagiarius primarily in Latin-language texts and in treatises that draw on the Corpus Juris Civilis. A few specific navigational notes:
First, the term does not migrate into common law. English common law developed its own vocabulary for kidnapping and abduction; plagiarius appears in English legal writing only when authors are consciously citing Roman law sources, as Blackstone does. Finding it in an English-language source almost always signals a civil law digression or a comparative passage.
Second, the Rapalje & Lawrence entry is the most substantively useful of the historical dictionary sources because it unpacks the full scope of the offense — covering not just abduction but also the downstream conduct of confinement, sale, or purchase. The Black's and Burrill entries give the shorthand (man-stealer; kidnapper) without capturing that the offense extended to buyers and sellers, not just the initial abductor.
Third, researchers should be alert to the etymological trap described above: the word "plagiarism" in its modern sense appears in English sources from the seventeenth century onward and has no legal content in that usage. Finding "plagiary" or "plagiarism" in a non-Latin legal text from the eighteenth century or later almost certainly refers to literary theft, not the civil law offense.
Fourth, for historical research into the legal status of freedmen and slaves in Roman law, plagium is a relevant offense because it treated the kidnapping of a freedman — a free person — as the same crime as the unlawful taking of another's slave, which raises comparative questions about legal personhood that appear in scholarship on Roman law and its reception.
Historical Dictionary Support
The four source dictionaries present substantially identical core definitions. All four agree on the Latin civil law context and on the pairing of "man-stealer" and "kidnapper" as the English equivalents. All four share the same authority trail: Dig. 48.15.1 and 4 Bl. Comm. 219.
Rapalje & Lawrence diverges usefully from the others by specifying the categories of conduct that constituted the offense under Roman law — knowing confinement in irons, sale, gift, or purchase of a freeborn person, freedman, or another's slave. This additional detail tracks the Digest more closely and is the more precise account.
What all four historical sources omit is any treatment of the penalties attached to plagium under Roman law, which were substantial (the offense was tried before the quaestiones perpetuae), or any discussion of the term's later reception in European civil law jurisdictions. Researchers needing that detail must go to Mommsen's Roman criminal law scholarship or to civilian treatises directly.
The co-listing of PLAGIARY and PLAGII CRIMEN in Rapalje & Lawrence under the same entry is editorially useful: it confirms that plagiarius (the person), plagiary (the English noun form), plagii crimen, and plagium (the offense itself) are all part of a single doctrinal cluster.