Justinian became universally famous because of his legislative work, remarkable for its sweeping character. It was his opinion that an emperor must be not only glorified with arms, but also armed with laws, so that alike the time of war and the time of peace may be rightly guided; he must be the strong protector of law as well as the triumpher over vanquished enemies. Furthermore, he believed, it was God who bestowed upon the emperors the right to create and interpret laws, and an emperor must be a lawgiver, with his rights sanctified from above. But, quite naturally, in addition to all these theoretical foundations, the Emperor was guided also by practical considerations, for he realized fully that Roman law of his time was in a very chaotic state.
Back in the days of the pagan Roman Empire, when the legislative power was entirely in the hands of the emperor, the sole form of legislation was the issuing of imperial constitutions, called laws or statute laws (leges). In contrast with these, all laws created by earlier legislation and developed by the jurists of the classical period were called jus vetus or jus antiquum. From the middle of the third century A.D., jurisprudence declined very rapidly. Juridical publications were limited to pure compilations, which aimed to assist judges unable to study the entire juridical literature by providing them with collections of extracts from imperial constitutions and the works of universally famous old jurists. But these collections were of a private nature and had no official sanction whatever, so that in real practice a judge had to look into all the imperial constitutions and into all of the classical literature, a task quite beyond the powers of any one man. There was no one central organ for the publication of the imperial constitutions. Increasing in quantity annually, scattered in various archives, they could not be used easily in practice, especially since new edicts very often repealed or changed old ones.