Final answer:
Justinian I created the Code of Justinian by consolidating Roman law and imperial decrees, which resulted in the Corpus Juris Civilis, laying groundwork for European legal systems.
Step-by-step explanation:
Emperor Justinian I utilized Roman law and imperial decrees to create his legal code, known as the Code of Justinian. His efforts were part of wider legal reform to consolidate and unify the various laws of the empire under a single system. Justinian mobilized legal experts to review the vast body of Roman law, eliminate contradictions, and decide which laws should be enforced. The result was the Corpus Juris Civilis, which became the foundation for many modern European legal systems. Additionally, Justinian preserved the use of Latin in legislation, underscoring continuity with Rome's legal legacy.