The civil law originated in ancient Rome. One of the principal characteristics of Roman civilization was the development of strong legal institutions. The principles and rules of Roman law were based partly on legislation and partly on the utterances of great legal scholars who were routinely asked for their opinions by judicial officers confronting difficult legal issues in the determination of lawsuits. In the 6th century a commission appointed by the emperor Justinian collected and consolidated all the sources of law, including the opinions rendered by the great legal scholars during previous centuries. The result was the Corpus Juris Civilis (Body of Civil Law), also called the Justinian Code, a comprehensive code embodying the accumulated wisdom and experience of many generations of Roman jurists.
Justinian’s realm was essentially limited to the eastern half of the Roman Empire; the western half had already been overrun by Germanic invaders. Thus, Justinian’s Corpus Juris had no immediate effect in western Europe, where the period from the 5th to the 10th century was one of cultural decline. In the course of the intellectual reawakening that occurred in the second half of the 11th century, the Corpus Juris was rediscovered in Italy. About the same time, the study of academic law was instituted at the newly founded University of Bologna, where the law professors based their teaching on the Corpus Juris. Other European universities followed suit, and the Justinian Code became an important element in the development of Continental law until relatively modern times. Other elements were canon law and the customs of merchants. Together they formed a body of written transnational law (known as jus commune) preserved by academic legal scholarship, with which lawyers and judges throughout continental Europe were familiar. Eventually, local statutes and numerous local customs, often of Germanic origin, were also committed to writing. In the frequent cases in which these local statutes and local customs did not furnish an answer, however, courts and lawyers tended to be guided by the transnational jus commune.
During the 17th and 18th centuries the authority of the Corpus Juris began to decline as its rules were re-examined in the light of reason. The stage was then set for the systematic and comprehensive codification of modern civil law. The most influential, although not the first, codification effort was the enactment, during the Napoleonic period, of the five basic codes of France: the Civil Code (Code Napoléon of 1804), the Code of Civil Procedure (1807), the Commercial Code (1808), the Penal Code (1811), and the Code of Criminal Procedure (1811). In the course of the 19th century, most civil-law countries similarly codified the bulk of their legal statutes. The German Civil Code (effective in 1900) and the Swiss Civil Code (1907) both exerted influence the world over.
Codification of the civil law had several major consequences. After their enactment, the codes constituted comprehensive and authoritative legal texts that superseded all earlier authorities in the teaching of law as well as in legal practice. Within each nation state, the codes brought about a strong measure of national unification of the law. Such unification, along with systematization and reform, enhanced the certainty and predictability of the law. In their substance, the codes differed from one nation to another, thus marking a shift from the transnational jus commune to separate national legal systems. In recent years, however, vigorous efforts have begun, in the nations of the European Union and elsewhere, to replace certain isolated national laws with international legal practices.