Common law
The common lawso named because it was "common" to all the king's courts across Englandoriginated in the practices of the courts of the English kings in the centuries following the Norman Conquest in 1066. The British Empire spread the English legal system to its historical colonies, many of which retain the common law system today. These "common law systems" are legal systems that give great precedential weight to common law, and to the style of reasoning inherited from the English legal system.
Law
Civil law is the legal system used in most countries around the world today. In civil law the sources recognised as authoritative are, primarily, legislation—especially codifications in constitutions or statutes passed by government—and custom. Codifications date back millennia, with one early example being the Babylonian "Codex Hammurabi". Modern civil law systems essentially derive from the legal practice of the 6th-century Eastern Roman Empire whose texts were rediscovered by late medieval Western Europe. Roman law in the days of the Roman Republic and Empire was heavily procedural, and lacked a professional legal class. Instead a lay magistrate, "iudex", was chosen to adjudicate. Decisions were not published in any systematic way, so any case law that developed was disguised and almost unrecognised. Each case was to be decided afresh from the laws of the State, which mirrors the (theoretical) unimportance of judges' decisions for future cases in civil law systems today. From 529–534 AD the Byzantine Emperor Justinian I codified and consolidated Roman law up until that point, so that what remained was one-twentieth of the mass of legal texts from before. This became known as the "Corpus Juris Civilis". As one legal historian wrote, "Justinian consciously looked back to the golden age of Roman law and aimed to restore it to the peak it had reached three centuries before." The Justinian Code remained in force in the East until the fall of the Byzantine Empire. Western Europe, meanwhile, relied on a mix of the Theodosian Code and Germanic customary law until the Justinian Code was rediscovered in the 11th century, and scholars at the University of Bologna used it to interpret their own laws. Civil law codifications based closely on Roman law, alongside some influences from religious laws such as canon law, continued to spread throughout Europe until the Enlightenment; then, in the 19th century, both France, with the "Code Civil", and Germany, with the "Bürgerliches Gesetzbuch", modernised their legal codes. Both these codes influenced heavily not only the law systems of the countries in continental Europe (e.g. Greece), but also the Japanese and Korean legal traditions. Today, countries that have civil law systems range from Russia and China to most of Central and Latin America. With the exception of Louisiana's Civil Code, the United States follows the common law system described below.