How did the roman law system work?

(Note: If you have a truly valid addition, add it, but do not change or subtract the current answer.)

There are three basic types of law:

Civil Law - that which relies on a codification of law in writing rather than judicial precedent

Common Law - that which relies on precedents of previous decisions of judges based on historic customs.

Criminal Law - that which operates on legislated prohibitions of certain conduct.

Originally Roman law was unwritten, which gave the aristocracy, the custodians of it, a decisive edge which, allied to their being also custodians of the state religion, gave them enormous power to control the populace. Agitation led to a codification called the Twelve Tables. This was followed over the centuries by codifications of additional laws by eminent jurists, essentially the process of conversion from customary (Common) law to civil law. The process was virtually completed by the 4th Century CE.

Today's Civil Law rests on the Roman precedents with later developments over 1,500 years, just as the the Roman Civil Law developed over a thousand years.