During the Byzantine Empire the Justinian Code was expanded and remained in force until the Empire fell, though it was never officially introduced to the West. Instead, following the fall of the Western Empire and in former Roman countries, the ruling classes relied on the Theodosian Code to govern natives and Germanic customary law for the Germanic incomers - a system known as folk-right until the two laws blended together.
After the Norman conquest of England, which introduced Norman legal concepts into mediaeval England, the English King's powerful judges developed a body of precedent that became the common law.