Corpus Iuris Civilis

Mosaic of Justinian in San Vitale, Ravenna
At the beginning of his reign the Roman emperor Justinian (527-565 A.D.) established  a ten-man commission chaired by John the Cappadocian to produce a new code of Roman law. The commission first produced a new compilation of the statutes and constitutions of the emperors, the Codex Justinianus (Codex vetus) that Justinian promulgated on 7 April, 529.
 

Then Justinian ordered the codification of  the legal opinions of the Roman jurists from ca. first century B.C. to the third century A.D. . On 15 December 530 he  ordered a commission to work at it: sixteen lawyers from the legal fraternities of Constantinople and Beirut, men headed by Tribonian, who had already been a member of the commission that produced the Codex Justinianus. The result of their labor was published on 16 December, 533. It was called the Digestum (Digest), or to give it its Greek name, the Pandects. The Digest contained the collective jurisprudence of  almost a millennium of Roman legal thought.  It would become the most important legal book ever produced and would influence the future shape of European and world jurisprudence.  At the same time, a committee also headed by Tribonian was working on a textbook for law students, the Institutes.  It was published  on 16 November. One byproduct of all this labor was to make the Codex vetus obsolete, and hence a new edition was published on 16 November, 534 and the first edition has failed to survive. This body of law and jurisprudence has been known since the sixteenth century as the Corpus Iuris Civilis.  Justinian intended it to be a unified body of law.   In December 533 the commission also published the Institutes, which was a textbook to be used  for first year students.

Justinian forbade commentaries on the Digest and probably the rule applied to the whole Corpus.

Most recent work on the Digest is Tony Honoré, Justinian's Digest: Character and Compilation (Oxford University Press, 2010)

The last part of Justinian's codification was the Novels  They were new laws that he issued after the Corpus was published.  The language of these constitutions was Greek.   He may  have planned a collection of his own legislation, but they were only put together as a collection until after his death.