The Code of Hammurabi is one of the earliest known written laws in history (1780 BC), taking credit for the concept of "an eye for an eye, a tooth for a tooth". It is pretty clear that this is how the judicial system came from that concept.
Roman law was an important part of Roman civilization. As one of the centers of knowledge back then, Romans came up with ways to organize, improve, study, write, and compile their laws. Roman law eventually made its way to Europe, and became one of the major influences in the continent's legal systems. While some parts of England were influenced by Roman Law, some decided to stick to the existing laws, which later on helped develop the English Common Law. The English Common Law was then spread by the British around its colonies, including the US.
