Short answers, pulled from the story.
The Twelve Tables, dating from the mid-fifth century BC, are the first written legal text of Roman law. Ten tablets were produced in 450 BC by ten citizens called the decemviri legibus scribundis, and two more were added in 449 BC. They did not constitute a complete legal code but instead targeted specific points of customary law, with the largest share of provisions devoted to private law and civil procedure.
The Corpus Juris Civilis is a comprehensive codification of Roman law ordered by the Eastern Roman emperor Justinian I. It was compiled between 529 and 534 AD and brought together statutes, classical juristic writings, and imperial pronouncements into a single body of law. It remained the basis of legal practice in the Byzantine Empire and influenced legal systems from Greece to Ethiopia.
Roman law spread through medieval Europe largely after a manuscript of the Digest was rediscovered in Italy around 1070. Scholars called glossators began annotating the ancient texts, and study centered on Bologna, whose law school grew into Europe's first university. By the mid-16th century, a system known as ius commune, blending Roman law with canon and Germanic custom, dominated legal practice across continental Europe and Scotland.
England's legal system was already more developed than most continental counterparts when Roman law was rediscovered around 1070, so Roman law's practical advantages were less obvious to English practitioners. English lawyers trained at the Inns of Court in London rather than at civil and canon law faculties. As a result, an independent common law tradition developed in parallel, though elements of Roman law entered English equity courts and some Roman concepts influenced the common law.
Rome's most important contribution to European legal culture, according to the Roman legal tradition itself, was not individual statutes but the emergence of a class of professional jurists known as the prudentes, and of law as a science. These jurists applied the methods of Greek philosophy to law, a subject Greek thinkers had never treated scientifically. Classical jurists such as Gaius, Ulpian, Paulus, and Papinian produced works that shaped European law for more than a thousand years after their deaths.
Many concepts from the Roman constitution survive in modern constitutional systems, including checks and balances, the separation of powers, vetoes, filibusters, quorum requirements, term limits, impeachments, the power of the purse, and regularly scheduled elections. The block voting found in the United States electoral college also traces to ideas in the Roman constitution.