Byzantine Emperor Justinian's MOST significant political accomplishment was

the codification and consolidation of Roman law. Justinian is best known for his efforts to reform and systematize Roman law, resulting in the creation of the Corpus Juris Civilis, or the Body of Civil Law. This legal code became the basis for modern legal systems in Europe and influenced legal thought throughout the centuries. It included legislation, legal opinions, and summaries of legal principles from Roman jurists. The codification of laws helped to restore order and stability in the Byzantine Empire and ensured a uniform application of laws throughout the empire. Additionally, Justinian's legal reforms helped to establish his legacy as a lawgiver and significantly influenced the development of Western legal systems.