Definition
In old English law, a horse-load — the quantity of goods or commodities that a single pack-horse was capable of carrying. The term functioned as a unit of measure for tolls, renders, and customary dues assessed on goods transported by packhorse, particularly through forests, markets, and along established routes. The precise weight or volume constituting a summagium was not fixed universally but varied by locality and by the type of commodity being transported.
Why It Matters in Research
Summagium appears almost exclusively in medieval English records — forest charters, manorial custumals, toll schedules, and administrative records of the Norman and Plantagenet periods. Researchers working with these sources need to recognize it as a unit of measure with legal and fiscal significance, not merely a descriptive term. Where a lord, crown, or forest authority had the right to levy tolls, the summagium could define the taxable unit: one horse and its load, rather than a count of individual items or a weight-based measure.
The term's relevance is largely confined to the medieval period. By the time English law had developed a settled literature of treatises and commentaries, summagium had receded from active use. It will not appear in Blackstone, Coke, or the later common law dictionaries that dominate most legal research collections. Researchers encountering the term in a translated or abstracted source should treat it as a signal that the underlying document is of considerable antiquity, likely pre-fifteenth century.
The forest charter context is particularly important. The Carta de Foresta (Charter of the Forest, 1217) and related documents regulated movement through royal forests, including the passage of goods. References to summagium in that framework are typically about rights of transit and the tolls or exemptions attached to them — not about ownership of the goods themselves.
Historical Dictionary Support
Burrill's Law Dictionary provides the only entry among Law Mind's shelf sources. Burrill traces the term to the Latin summa (a sum, a load, a beast of burden's burden) and defines it concisely as "a horse-load," supporting the definition with a direct reference to the Carta de Foresta, chapter 14: Pro equo qui portat summagium — "for a horse that carries a summagium." This single citation is characteristically precise for Burrill and anchors the term firmly in forest law administration.
No other Law Mind historical dictionary covers summagium, which itself reflects the term's narrow medieval scope. Spelman's Glossarium (outside the current corpus) would be the natural extended reference for a term of this character, as it was designed specifically for post-classical Latin legal and administrative vocabulary of English records. Researchers who exhaust the Law Mind corpus on this term should expect to move quickly to Du Cange's Glossarium Mediae et Infimae Latinitatis, the standard reference for medieval Latin, where summagium and related forms (sagma, sagmarius) receive fuller treatment in their continental as well as English contexts.
The relationship between summagium and the broader family of toll-and-passage terminology — including the right of sommage or saumage recognized in French customary law — is not addressed in Burrill, but may be relevant when working with Anglo-Norman records where French and Latin legal vocabularies overlap.
Jurisdictional Note
Summagium is a term of English medieval law with particular concentration in forest administration and manorial records. It has no recognized equivalent or parallel usage in Scots law, Irish law, or the civilian tradition, though cognate terms appear in French customary sources under different forms.