Reddit mentions of The Anglo-American Legal Heritage: Introductory Materials

Took a course on legal history in law school, so I know a bit but I'm in no ways a scholar on this. Your question greatly depends on what country you're asking about. Generally, there are three major types of legal systems in the world today: civil law, common law, and sharia law.

Civil law is the most common system and is used in countries like France, Germany, etc. Common law is used by countries like the United States and India. Interestingly, the only countries in the world today that use common law were once British colonies. Sharia law is law based off the Quran.

Assuming your question is in regards to the US, our legal tradition is largely based on the English common law system. Common law originated in England, but it certainly didn't "grow" out of Roman law.

The western world's legal systems collapsed with the fall of the Roman Empire. Rome had a surprisingly robust and complex legal system which we know of thanks to Justinian's Code, which was one Roman emperor's attempts to condense the very complex and fragmented Roman legal system into three volumes.

When the Roman Empire collapsed, legal systems across Europe fell back into simplistic systems like an eye-for-an-eye. There's an old English code out there that specifically states each specific crime and its punishment (e.g., caught stealing you lose a hand), but I forgot the name of it. Either way, it remains an example of how far law regressed after the fall of the Roman Empire. It's from this collapsed system that the common law grew. As England grew, its legal system grew increasingly complex with it. The most significant development from it was where judicial precedent was valued as a tool for interpretation. This basing our interpretation of the law on precedent is basically what we call common law today.

It's worth noting that the US legal system is quite a bit different from the Enlgish one today, but we actually have some more traditional elements that England has done away with, like the Grand Jury.

If you want to read more into it:
https://www.amazon.com/Anglo-American-Legal-Heritage-Introductory-Materials/dp/1594600384