Definition
A Latin term meaning emperor or supreme commander, used in legal and historical sources to denote a sovereign ruler holding paramount authority. In Roman law, the title identified the emperor as the supreme source of legal authority — the sole maker and interpreter of law. The maxim recorded in the Codex captures this precisely: *Imperator solus et conditor et interpres legis existimatur* — the emperor alone is considered the maker and interpreter of the law. In English legal history, the term appears in pre-Conquest royal charters, where Anglo-Saxon kings occasionally styled themselves with the title as a claim to overlordship.
Common Language
Modern common usage (Wiktionary): An emperor.
Historical common usage (Webster's 1913): A commander or leader; originally a title of honor conferred by Roman soldiers upon their general after a significant victory; later formalized by the Senate as recognition of military achievement; eventually assumed by Augustus and his successors as a permanent imperial designation.
The gap between common and legal usage here is historical rather than definitional. Where ordinary usage treats *imperator* simply as a synonym for emperor, the legal sources invest the term with a specific constitutional weight — locating in the emperor the exclusive power to make and interpret law. Researchers encountering the term in Roman law sources should read it not merely as a title of rank but as a marker of sovereign legal authority.
Why It Matters in Research
This term functions differently depending on whether the researcher is working in Roman law sources, medieval English sources, or early modern legal theory.
In Roman law materials — the Institutes, the Digest, and especially the Codex — *imperator* carries the full weight of the principle that law originates in and returns to the emperor. The maxim at Cod. 1.14.12 is foundational to understanding why Roman legal texts treat imperial rescripts and constitutions as binding authority. Researchers tracing theories of sovereignty, statutory interpretation, or the sources of law in civilian tradition will encounter this term as a load-bearing concept, not mere honorific.
In English legal history, the appearance of *imperator* in pre-Conquest charters is a distinct phenomenon. Anglo-Saxon kings used the title to assert supremacy over other rulers within Britain — it was a political claim, not a Roman legal inheritance in any strict sense. Blackstone's discussion (1 Bl. Comm. 242) addresses this usage. Researchers working with early English constitutional sources should not read the Anglo-Saxon use as importing Roman legal doctrine; the term traveled as prestige vocabulary, not as legal framework.
A research trap: later legal theorists and canonists debated whether kings held *imperium* — supreme power — within their own kingdoms, invoking Roman law categories. The phrase *rex est imperator in regno suo* (the king is emperor in his own kingdom) became a contested formula in medieval and early modern arguments about papal versus royal jurisdiction. Researchers in that literature will encounter *imperator* and *imperium* as terms of art in sovereignty debates, requiring care not to conflate their technical use with either the Roman constitutional meaning or the Anglo-Saxon honorific usage.
Historical Dictionary Support
All three historical dictionaries agree on the core: *imperator* means emperor, the title of Roman emperors, and was also applied to pre-Conquest English kings. Burrill provides the most substantive legal content, quoting the Codex maxim directly and citing Taylor's *Elements of Civil Law* for additional context — giving the term its proper weight as a marker of legislative and interpretive supremacy in Roman law. Black's and Bouvier's are briefer, treating the term primarily as a title of address and directing readers to their entries for EMPEROR.
None of the three historical dictionaries addresses the term's role in medieval sovereignty theory or the *rex in regno suo* formula — a gap that matters for researchers working in ecclesiastical law, early modern jurisprudence, or the history of international law, where the concept migrated well beyond its Roman constitutional origin.
Encyclopedia Cross-Reference
See Law Mind Encyclopedia: Roman Law; Sovereignty; Sources of Law (Civil Law Tradition)