The Theodosian and Justinian Codes show the drastic change of the concept of imperial rescript in the course of 4-6th centuries AD. Though the Theodosian Code considers imperial rescript as one of the sources of law, the Justinian Code does not admit the rescript into the category of legal sources. The Roman emperors of the 4th century AD issued their rescripts in total conformity with the classical Roman tradition to develop existing legal institutions by interpreting outdated legal rules and principles. However, the necessity of providing a reliable source of law forces Roman emperors to enact statutes in more general form than rescripts. The transition from rescript to general enactment (lex generalis} as a chief form of imperial legislation is complete under Justinian.