The Institutes of Justinian ( or "Justinian's Institutes") is a unit of the Corpus Juris Civilis, the sixth century codification of Roman law ordered by the Byzantine emperor Justinian I. It is largely based upon the Institutes of Gaius, a Roman jurist of the second century A.D. The other units in the Corpus Juris Civilis are: the Digest, the Codex Justinianus, and the Novellae Constitutiones ("New Constitutions" or "Novels").