After the establishment of the empire, the development of law largely passed from the praetors (the practice of issuing new edicts ended c.A.D. 125) and from the popular assemblies into the hands of the emperors, sometimes operating through the senate. Various types of imperial enactments called constitutions were issued in abundance.
Legal problems attained great complexity, and the aid of a specially trained class of scholars was enlisted for their solution. Those jurists with a special license from the emperor could write responsa to guide the judges in deciding cases. Most prominent among the jurists was Papinian; his work, with that of Gaius, Modestinus, Paulus, and Ulpian, attained the highest authority. The employment of jurists was a step in making the whole of Roman procedure official; in this process the institution of judex was abolished and the trial placed entirely in the hands of a judge.
By the early 4th cent. most branches of Roman law were fully developed. The system was generally responsive to legal needs and allowed sufficient variety to meet local customs. A grave disadvantage of the system, however, was that the vast corpus of legal matter included much that was confused, contradictory, or redundant; reduction to code form was required. The Theodosian Code (438), the earliest attempt, was followed by the Breviary of Alaric (506). Finally the task was accomplished with the culminating work of Roman legal scholarship, the Corpus Juris Civilis (completed 535) under the direction of Tribonian.