Short answers, pulled from the story.
Civil law is a legal system rooted in the Roman Empire and comprehensively codified starting in the 19th century. It relies on legal codes as the primary source of law, rather than judicial precedent. It is the world's most common legal system, practiced in about 150 countries.
Civil law takes the form of legal codes that function as the primary source of law, while common law comes from uncodified case law arising from judicial decisions that recognize prior court decisions as binding precedent. Civil law judges give less weight to judicial precedent, and the French civil law tradition has no doctrine of stare decisis. Common law originated in medieval England.
The Napoleonic Code of 1804, named after French emperor Napoleon, and Germany's Bürgerliches Gesetzbuch, which went into effect in 1900, are the most prominent examples. The Napoleonic Code comprises the law of persons, property law, and commercial law. The German Civil Code is divided into five parts and inspired civil codes in Japan, South Korea, and Switzerland.
Civil law is rooted in the Roman Empire, taking classical Roman law from roughly AD 1 to 250 and Justinian law of the 6th century AD as its major inspirations. It was further developed in the late Middle Ages under the influence of canon law. The term jus civile, meaning citizens' law, was the late imperial Roman term for its legal system.
Louisiana is the only U.S. state whose private civil law is based heavily on the French and Spanish codes rather than English common law. Its private law was codified into the Louisiana Civil Code. Over time it has converged with American law, including adoption of the Uniform Commercial Code except for Article 2.
Civil law codifications were completed across Europe, by Denmark in 1687, Sweden in 1734, Prussia in 1794, France in 1804, and Austria in 1811, then carried into colonies by most of these countries. French codes were adopted with modifications in places including Louisiana in 1807, the Netherlands in 1838, and Spain in 1888. The Swiss version was adopted in Brazil in 1916 and Turkey in 1926.