Definition
A historical English customs duty levied on wines and other imported or exported merchandise, assessed according to a fixed rate per ton of cargo. Tonnagium was an impost of the crown, collected at ports as a condition of trade, and belongs to the broader category of feudal and medieval revenue measures that predated the modern customs and excise system. The term appears in old English law and is primarily of historical and antiquarian significance.
Common Confusion
Tonnagium is related to but distinct from poundage (poundagium), a parallel impost levied on goods by weight or value rather than by unit of volume. The two duties were frequently granted together by Parliament to the crown and are sometimes collectively referenced in historical sources as "tonnage and poundage." A researcher encountering one term in a historical document should check for the other, as statutes and grants typically addressed both simultaneously. Neither term survives as an operative legal concept in modern law.
Why It Matters in Research
Tonnagium surfaces almost exclusively in pre-modern English legal materials — primarily statutes, royal grants, and treatises from the medieval and early modern periods. Researchers working in those sources should be aware of several navigational points.
First, the phrase "tonnage and poundage" was politically charged in seventeenth-century England. Charles I's collection of these duties without parliamentary authorization became a central grievance in the constitutional conflicts leading to the English Civil War. A researcher encountering tonnagium in that period may be dealing with constitutional controversy, not merely customs administration.
Second, the term's scope shifted over time. Originally associated closely with wine imports — reflecting the trade patterns of medieval England — it was later extended to merchandise more broadly. Historical sources may reflect different moments in this evolution, and a narrow definition drawn from one source may not hold for documents from another period.
Third, tonnagium as a word is Latinized law French, the standard drafting language of medieval English legal instruments. Variant spellings and forms appear across manuscript and printed sources. Researchers using keyword searches in digitized historical corpora should anticipate spelling variation (tonagium, tonageum, and similar forms).
Fourth, this term has no analogue in American law. The U.S. Constitution contains a distinct "Tonnage Clause" (Article I, Section 10, Clause 3), which prohibits states from levying duties on ships based on tonnage without congressional consent. That provision uses tonnage in a related but different sense — referring to the capacity or burden of vessels, not a specific medieval English impost. Researchers should not conflate the two.
Historical Dictionary Support
The four source dictionaries — Black's (both editions), Bouvier's, and Burrill's — are in near-complete agreement, with each defining tonnagium as a custom or impost upon wines and other merchandise, exported or imported, at a rate per ton. All four trace the term to the same authorities: Spelman's Glossarium Archaiologicum and Cowell's Interpreter, the standard seventeenth-century glossaries of old English and law Latin terms. The consistency across sources reflects that, by the time these dictionaries were compiled, tonnagium was already a historical artifact requiring scholarly reconstruction rather than practical exposition.
What the historical dictionaries do not provide is context: none address the constitutional history of tonnage and poundage, the parliamentary statutes that regulated or disputed the duty, or the administrative machinery of its collection. For that context, the dictionaries must be supplemented with English legal and constitutional history sources. Spelman and Cowell, cited in all four entries, remain the best primary glossary references for the term itself.
Jurisdictional Note
Tonnagium is a term of English law only and has no reception in American, Scottish, or other common law jurisdictions as a legal concept. The only American constitutional use of the word "tonnage" appears in the Tonnage Clause of Article I, which concerns vessel duties and is unrelated to the medieval English impost.