Short answers, pulled from the story.
The Law of the Twelve Tables marked the first written legal text for Rome and was established around 451 BC with a second group adding rules in 449 BC. This law ended unwritten private law bound to religious ritual after plebeians fought eight years to force patricians to share legal knowledge.
Gnaeus Flavius published formularies containing words required to begin legal actions around 300 BC that had been secret and known only to priests before his publication. These formulas supplemented existing civil law alongside edicts issued by praetors between 201 BC and 27 BC.
Justinian decreed a comprehensive code between 529 and 534 AD covering existing laws that continued serving as the foundation throughout so-called Byzantine history despite political changes. The Codex Theodosianus codified Constantian laws in 438 AD before these reforms while Greek language replaced Latin in official legislation from the seventh century onward.
A manuscript of the Digest was rediscovered in Italy around 1070 by scholars called glossars who added comments between lines or in marginal notes to ancient texts. Bologna became the center for studying these recovered Roman legal documents where the law school developed into Europe's first university teaching complex economic transactions.
Today South Africa and San Marino maintain legal systems still based on old jus commune principles while Germany applied Roman law until its Bürgerliches Gesetzbuch went into effect in 1900 after centuries of usus modernus Pandectarum influence. Legal systems across Latin America and former colonies inherited these continental practices through colonial expansion without any complete code breaking entirely with Roman tradition.