Today, Roman law is no longer applied in legal practice, although the legal systems of some countries such as South Africa and San Marino are still based on the former municipality of ius. But even when legal practice is based on a code, many rules derived from Roman law apply: no code has completely broken with Roman tradition. On the contrary, the provisions of Roman law have been inserted into a more coherent system and expressed in the national language. For this reason, knowledge of Roman law is essential to understanding today`s legal systems. Thus, Roman law is often still a compulsory subject for law students in civil law jurisdictions. In this context, the Moot Court of International Law has been developed annually to better educate students and to network with each other internationally.    The codices of Justinian, especially the Corpus Juris Civilis (529-534), continued to form the basis of legal practice in the empire throughout so-called Byzantine history. Leo III the Isaurian issued a new code, the Ecloga, at the beginning of the 8th century. In the 9th century, Emperors Basil I and Leo VI the Wise commissioned a combined translation of the Codex and the Digest, parts of the Justinian codes, into Greek, which became known as the basilica. Roman law, as preserved in the codes of Justinian and in the basilica, remained the basis of legal practice in Greece and in the courts of the Eastern Orthodox Church even after the fall of the Byzantine Empire and the conquest by the Turks and, together with the Syro-Roman code of law, also formed the basis of much of the Fetha Negest. which remained in force in Ethiopia until 1931. The first text of the law is the Law of the Twelve Tablets of the middle of the fifth century BC. J.-C.
The plebeian tribune, C. Terentilius Arsa, proposed writing the law to prevent judges from arbitrarily applying the law.  After eight years of political struggle, the plebeian social class convinced the patricians to send a delegation to Athens to copy Solon`s laws; For a similar reason, they also sent delegations to other Greek cities.  In 451 BC. According to traditional history (as Livy relates), ten Roman citizens were chosen to register the laws known as decemviri legibus scribundis. While performing this task, they were given supreme political power (imperium), while the power of magistrates was limited.  In 450 BC. The decemviri produced the laws on ten tablets (tabulae), but these laws were considered unsatisfactory by the plebeians.
A second decemvirate is said to have added two more tablets in 449 BC. J.-C. The new Law of the Twelve Tablets has been approved by the People`s Assembly.  Lawyers have also produced all sorts of legal sanctions. Around 130 AD, the jurist Salvius Iulianus drafted a standard form of praetorian edict, which was used by all praetors from that time on. This edict contained detailed descriptions of all cases in which the praetor authorized a claim and in which he granted a defense. The standard edict thus functioned as a complete legal code, even if it did not formally have the force of law. He stressed the prerequisites for a successful trial. The edict thus became the basis for many legal commentaries by later classical jurists such as Paul and Ulpian. The new legal concepts and institutions developed by preclassical and classical jurists are too numerous to mention here. Here are a few examples: the adaptation of the law to new needs has been entrusted to legal practice, judges and, above all, lenders.
A praetor was not a legislator and technically did not create a new law when he issued his edicts (magistratuum edicta). In fact, the results of its judgments enjoyed legal protection (actionem dare) and were often the source of new laws. The successor of a praetor was not bound by the edicts of his predecessor; However, he adopted rules drawn from the edicts of his predecessor that had proved useful. In this way, a constant content was created, which went from edict to edict (Edictum traslatitium). Traditionally, the origins of Roman jurisprudence are associated with Gnaeus Flavius. Flavius is said to have published around 300 BC. J.-C. the formulas with the words that had to be pronounced in court to bring a lawsuit. Before the time of Flavius, these formulas would have been secret and known only to priests.
Their publication allowed non-priests to explore the meaning of these legal texts. Whether this story is credible or not, jurists were active and legal treatises were written before the 2nd century BC. Written in greater numbers. Among the famous jurists of the Republican period are Quintus Mucius Scaevola, who wrote a vast treatise on all aspects of law, which later had a great influence, and Servius Sulpicius Rufus, a friend of Marcus Tullius Cicero. Thus, Rome had developed a very sophisticated legal system and a refined legal culture when the Roman Republic was replaced by the monarchical system of the Principate in 27 BC. The surviving fragments show that it was not a legal code in the modern sense of the term. It did not contain a complete and coherent system of all applicable rules, nor legal solutions for all possible cases. On the contrary, the tables contain specific provisions modifying customary law existing at the time. Although the provisions cover all areas of law, most of them are devoted to private law and civil procedure.
The constitution of the Roman Republic, or mos maiorum (“custom of the ancestors”), was an unwritten set of directives and principles transmitted mainly by precedents.