Justinian became coemperor of the Byzantine Empire with his uncle Justin in . Later that year, when his uncle died, he became sole emperor. Probably even while Justin had been sole ruler, Justinian was contemplating a legal codification of some kind. He issued a constitution dated February , , establishing a commission to prepare a new collection, aCodex, of imperial constitutions. The word “constitution” here is a general term to include all kinds of imperial legal rulings. The compilers were given extensive powers to collect the constitutions, to omit any, in whole or in part, that were obsolete or unnecessary, and to remove contradictions and repetitions. They were not given power to make alterations in substance. The constitutions were then to be arranged by subject matter in titles, or named chapters, and within each title the constitutions were to be given in chronological order. TheCode, which was published on April , , has not survived, but it was replaced by a second revised Code, which came into effect on December , . The revisedCode, which has survived and is one of the four constituent elements of what came to be called the Corpus Iuris Civilis, is divided into twelve books, subdivided into titles in which the constitutions appear chronologically. The constitutions range in date from Hadrian in the early second century to Justinian himself. A considerable proportion of the texts -  as against  - come from the time after the Empire became Christian; in fact, the bulk of the Christian rescripts is much greater. On December , , Justinian ordered the compilation of a collection of juristic texts, the Digest, and the work came into force on December , . This massive work, twice the size of the Code, is in fifty books, virtually all of which are subdivided into titles. Each title consists of fragments from the writings of jurists who lived between the first century B.C. and the third century A.D. About one-third of the whole work is taken from the jurist and civil servant Ulpian, who 