 Early in his reign , Justinian appointed the quaestor Tribonian to oversee this task . The first draft of the Codex Iustinianus , a codification of imperial constitutions from the 2nd century onward , was issued on 7 April 529 . ( The final version appeared in 534 . ) It was followed by the Digesta ( or Pandectae ) , a compilation of older legal texts , in 533 , and by the Institutiones , a textbook explaining the principles of law . The Novellae , a collection of new laws issued during Justinian 's reign , supplements the Corpus . As opposed to the rest of the corpus , the Novellae appeared in Greek , the common language of the Eastern Empire . 
