The Roman law which had a significant impact on the early Middle Ages was not the law which was in force during the decline of Rome's civilization. The author discusses why the Vulgar law was well suited for early medieval culture and why the classical Roman law was only revived toward the end of the Middle Ages.
The Influence of Roman Law on Early Medieval Culture,
3 Hastings Int'l & Comp. L. Rev. 9
Available at: https://repository.uchastings.edu/hastings_international_comparative_law_review/vol3/iss1/2