Most western legal systems are based on what ancient law?

Most Western legal systems are either based on Roman law or on Common law. Roman law is the predominant one throughout Europe, and represents a more coherent law. Many countries based on this system also later adopted the Code Napoléen, Napoleon's legal system, which represents an attempt to create one comprehensive legal framework. Common law, on the other hand, is mainly practiced in The UK and in the USA, though especially the latter also contains elements of Roman law. Common law, while not necessarily inferior, is less comprehensive. Rather than one legal framework, it is an amalgam of laws that were formulated over the years. Rather than one legal text, such as the German "Bürgerliches Gesetzbuch" it is thus a collection of bills and amendments which exist independently of each other.