Ancient Rome is the origin of civil law, and you've got continuity in Roman law for the entire existence of Rome--and Byzantium. Some parts of Roman law survived pretty solidly intact, and even got copied over into common law countries. I was actually talking about Somalia, and I've seen a good argument that it's part of why Italy's attempt to colonize the place failed hilariously. When the people you're trying to colonize are thinking somebody's dumped a bunch of tards on 'em... It was probably not helped by being an admittedly reasonable mistake. (It also kind of explains a lot about Somalia.)
The reason we got public prosecutors, though? That was because it was realized there might be a few problems with letting anybody who had the time free, interest, and (maybe!) resources step into the job. You weren't even required to be a lawyer...though, admittedly, it also meant if a case wasn't getting prosecuted it was because nobody was willing or able to do so.
If that hadn't changed? We'd be at risk of an arc about...most likely Wedge...deciding to be a volunteer public prosecutor.