Hey,
You can divide European law into two groups, which you can divide into subgroups: -continental group (germanic circle), (romanic circle), (nordic circle), -common law group (England and Wales - not whole UK (Scotland is abit different)
Why did the two groups who started from the same root differentiante so much you might ask. There are two important factors for that: -reception of Digeste (Justinian's codification - Roman law) 11th-12th century, -codification (Napoleonic codifications, ABGB ...) 18th-19th century
Before reception there were no major differences between continent and british isles in terms of perception of law.
After the Digeste were rediscovered in 11th-12th century whole continental Europe studied cases in them and then developing new rules building on knowledge from Roman Iurists. This was studied on univiersities all across Europe so there was law that was standard for whole continent called Ius Commune. Although its use was subsidiary it became more and more used as it was seen as more fair and reasonable then local traditons.
Since that didn't happen in Britain - common law was always about the proccedure not material rights there was no need to study Digeste at such scale - the two legal systems started driffting apart.
So before the era of codifications the law was standard across whole continental Europe. With the codification the Iurists didn't invent new law - they just codified the already present Ius Commune.
Although it may seem that todays law differs from country to country in Europe alot that is only partly true. Because all the codifications originate from the same all-continental law they are very similar in their core and offer similar solutions to similar problems, use simiar terminology etc.
Hope that answer helps.
Following on the post just made, Napoleon largely updated and republished the Roman law, the Code Justinian. I'm not sure that I agree that law was uniform across the continent prior to that, but Napoleon's actions in doing that, given his place in time, did have a very large impact.
Your question basically asks if there was anything like Common Law on the continent at some point, and the answer would be yes, but you'd have to go back well before the Napoleonic Era. The Germanic and Nordic cultures all used a type of common law early on, much of which was basically self administering. If you want to read a dramatic account of who it tended to work the Icelandic Sagas, interestingly enough, provide examples as much of what was going on with them had to do with that culture's perceptions of the operation of their laws, none of which differed greatly from one culture to another in Northern Europe, at various points. Clearly, they did differ some and certainly differed as the cultures came under the influence of Christianity.