In the 5th century BC, slavery in Rome reached the highest level, and Roman jurisprudence reached a higher level. At this time, jurists were divided, and a few became advisers to Roman rulers or served as court advisers. At that time, Roman law stipulated that in civil litigation, another citizen other than the party was allowed to represent the defendant against the plaintiff in court. In the Roman Empire, both the original defendant and the defendant in criminal cases were allowed to hire legal experts as defenders to argue in court. Therefore, most jurists become practicing civil litigation agents or criminal litigation defenders according to the law, which is the earliest lawyer in the history of the world.