The first of these comprised: (i.) all such of the statutes (leges) passed under the republic and early empire as had not become obsolete; (ii.) the decrees of the senate (senatus consulta) passed at the end of the republic and during the first two centuries of the empire; (iii.) the writings of the jurists of the later republic and of the empire, and more particularly of those jurists to whom the right of declaring the law with authority (jus respondendi) had been committed by the emperors.
The instructions given to them by the emperor were as follows: - they were to procure and peruse all the writings of all the authorized jurists (those who had enjoyed the jus respondendi); were to extract from these writings whatever was of most permanent and substantial value, with power to change the expressions of the author wherever conciseness or clearness would be thereby promoted, or wherever such a change was needed in order to adapt his language to the condition of the law as it stood in Justinian's time; were to avoid repetitions and contradictions by giving only one statement of the law upon each point; were to insert nothing at variance with any provision contained in the Codex constitutionum; and were to distribute the results of their labours into fifty books, subdividing each book into titles, and following generally the order of the Perpetual Edict.2 These directions were carried out with a speed which is surprising when we remember not only that the work was interrupted by the terrible insurrection which broke out in Constantinople in January 532, and which led to the temporary retirement from office of Tribonian, but also that the mass of literature which had to be read through consisted of no less than two thousand treatises, comprising three millions of sentences.