In the early days of the country's formation, there was no written code in Rome, only customary law, which was not explicitly recognized by the government and accepted by ordinary people. By default, it was the rule of mutual relations in social life. Because the customary law has no fixed written form, it has great flexibility and uncertainty. However, the limitations of this legal system in ancient times, when the judicial system was backward, often led to the inaccuracy of legal norms, which virtually provided convenience for judges to deliberately oppress civilians and protect nobles. In order to change this unequal status, in the early days of Rome, the common people organized themselves to put pressure on the government to compile written laws. The law of twelve bronze watches, the first written code in Roman history, was promulgated in 450-449 BC, which was the result of the people's struggle against the nobility. The Law of Twelve Copper Tables contains a wide range of contents, including public law and private law, criminal law and civil law, substantive law and procedural law, homomorphic revenge and fines, clan inheritance and will, etc. To some extent, it limited the tyranny and abuse of power of the nobility. Since then, with the continuation of the struggle between civilians and nobles, Rome has further adjusted the class relationship between citizens and continuously promoted the continuation of national legislation.

Judging from the legal content, the scope of application of Roman law before the middle of the 3rd century BC was limited to Roman citizens, and foreigners living in Rome could not enjoy the protection of this law. It is called civil law or civil law, and its content is mainly about Roman administration, state organs and some litigation procedures. There are obvious defects in the Civil Law, which are mainly manifested in the narrow scope of legal subjects, conservative content, strong formalism and a large number of clan remnants. With the expansion of Rome's conquered areas, great changes have taken place in Rome's social politics and economy, and civil law is no longer enough to solve all kinds of complex problems within the imperial territory. In Rome, a law that is generally applicable to all free people within the scope of Roman rule has gradually formed, which is the famous law of peoples.