Justinian I. Flavius Anicius Justinianus, nephew, on the mother's side, of the Emperor Justin, was born in 482 or 483 A.D., in the village of Tauresium, in Illyria. His original name was Uprauda. Although of obscure parentage, the son of a Slavonic peasant, he shared the success of his maternal uncle, Justin, being invited at an early age to Constantinople, where he received a careful education. When his uncle assumed the purple in 518 he appointed Justinian commander-in-chief of the army of Asia. His tastes, however, inclining him rather to civic pursuits, he declined this appointment, and remained attached to the court of Constantinople. In 521 he was named consul, and during the remaining years of the reign of his uncle he continued to exercise great influence. In 527 the Emperor Justin, by the advice of the senate, proclaimed him his partner in the empire.
Justin survived this step but four months, and in the same year Justinian was proclaimed sole emperor, and crowned along with his wife, the famous Theodora, whom, despite of her more than dubious antecedents as an actress, he had raised to the position of his wife. Justinian, on his accession, was in his forty-fifth year. His reign, which extends over thirty-eight years, is the most brilliant in the history of the late empire. Although himself without the taste or the capacity for military command, he had the good fortune or the skill to select the ablest generals of the last days of Roman military ascendancy. Under the direction of his generals, and especially of the celebrated Narses (q.v.) and Belisarius (q.v.), his reign may be said to have restored the Roman empire, at least in outward appearance, to its ancient limits, and to have reunited the East and West under a single rule. In his first war—that with Persia—he concluded a treaty by which the crisis that had so long threatened was at least warded off; but the rejoicings which celebrated its termination had, owing to a domestic revolution, almost proved fatal to the authority of Justinian himself. A conflict of the so-called Blue and Green factions in the circus in 532 was but an outburst of political discontent, which went so far as to elect a rival emperor, Hypatius. Justinian himself was struck with dismay, and had made preparations for flight; but the vigour and determination of Theodora arrested the revolt. Narses, with a relentless hand, repressed the tumults, 30,000 victims having, it is said, fallen in a single day. By the arms of Belisarius, the Vandal kingdom of Africa was re-annexed to the empire; and the same general, conjointly with Narses, restored the imperial authority in Rome, in Northern Italy, and in a large portion of Spain. One of the most extraordinary, though in the end ineffective works of the reign of Justinian was the vast line of fortifications which he constructed, or renewed and strengthened, along the eastern and south-eastern frontier of his empire. These works of defence, and the construction of many public buildings both in his capital and in other cities of the empire, involved an enormous expenditure, and the fiscal administration of Justinian, in consequence, pressed heavily on the public resources.
It is, however, as a legislator that Justinian has gained his most enduring renown. His good fortune in obtaining the services of able generals was not greater than that which attended him in the field of law and legislation. Brilliant as were the triumphs of Narses and Belisarius, they were indeed short-lived in comparison with the work done by the celebrated Tribonian (q.v.) and his coadjutors in the way of reforming and codifying the law. Immediately on his accession Justinian set himself to collect and codify the principal imperial constitutions or statutes enacted prior to, and in force at, the date of his accession. In this respect he followed the example set by his predecessor, Theodosian. The code in which these constitutions were collected was published in 528-29, and it contained a general provision by which all previous imperial enactments were repealed (see CODE). But Justinian's ambition in the matter of consolidating the laws went much further. Imperial constitutions made up but a comparatively small part of the body of the law. The bulk of it (what might be called the common law) was contained in the writings of the jurists—i.e. of text writers and commentators. Of these writings there were at this time many hundreds of volumes in existence, and, owing to want of agreement in the opinions of the various writers, the law was in a state of great uncertainty, not to say confusion. To remedy this evil Justinian resolved upon the publication of a single treatise in which the commentaries and other writings of the jurists might be digested and harmonised. The preparation of this great work was entrusted to Tribonian, with the assistance of Theophilus, a celebrated professor of law at Berytus (modern Beyrout), and two other professors, and eleven advocates, and it was completed in the short period of four years. It was published in fifty books under the title Digesta or Pandectæ on 31st December 534. While the Digest was in course of preparation Justinian resolved on the composition of a third legal work—viz. a systematic and elementary treatise on the law which might serve as a textbook for the use of students and as an introduction to the larger work. The preparation of this was also entrusted to Tribonian and his colleagues, and having been completed a few days before the Digest, was published in four books on the same day (31st December 534) under the title of Institutiones. It is based upon the Institutes of Gaius, and is familiar to all modern lawyers under the name of 'Justinian's Institutes.' Meanwhile, while both the Digest and the Institutes were being prepared, the Code of 529 above mentioned was withdrawn from circulation and republished in 534 with some alterations, and especially with the addition of fifty new constitutions (known as the Quinquaginta Decisiones) which had in the interim been pronounced by Justinian. This new edition, in twelve books, is known as the Code Repetitæ Prælectionis, and is the one which has come down to us, no copy of the earlier codex being extant. All these works (Code, Digest, Institutes) were written originally in Latin, and all of them were prepared with care and skill, and testify to the great ability of Tribonian and his co-editors. Upon the publication of the Digest Justinian declared by a constitution that all previous law books and decisions were to be held as superseded, and it was forbidden to refer to them in the practice of the courts. During the subsequent years of his reign Justinian pronounced from time to time several new constitutions or laws, some of them making very important changes in certain departments of the law. These (mostly in Greek) were collected and published under the title of Novellæ (i.e. 'the Novels' or 'New Constitution'). There were, so far as can be ascertained, about 170 of these Novels. The Institutes, Digest, Code, and Novels together make up what is known as the Corpus Juris Civilis.
The character of Justinian has been much canvassed, and opinions are not agreed about it. Procopius, in two separate works, has painted him in very different lights. Making allowance, however, for much exaggeration of his abilities by contemporary writers, it may be said that he contrasts favourably with most of the emperors, whether of the earlier or the later empire. If his personal virtues be open to doubt (and certainly vanity, avarice, and inconstancy were in no small degree characteristic of him), he, on the other hand, displayed undoubted ability as a ruler, and in the main, just and upright intentions. He died on 14th November 565 at the age of eighty-three, and in the thirty-eighth year of his reign.
A few words must be said about the legislative reforms carried through by Justinian. He was not only a collector and codifier of the laws; he also introduced in many directions the most fundamental changes into the substantive law itself. The following were the most important changes: (1) He ameliorated the condition of slaves—depriving their masters of the power of putting them to death. He declared that any one who put a slave to death at his own hand should be guilty of homicide. (2) He greatly revolutionised the law of intestate succession by giving to cognati (relatives on the mother's side) an equal share with agnati (relatives on the father's side) of the same degree. These two changes in the law were probably in a large measure induced by the circumstances of his birth. He made considerable changes in the law of divorce and as to the property of spouses, and he reformed civil procedure in the way of making it uniform, and introducing a system of small-debt courts.
See the Life by Isambert (Paris, 1856); by G. Body (6th ed. 1889); Newman, Doctrine of Justinian (4th ed. 1885); Roby, Introduction to the Digest (1884); Muirhead, Roman Law (1886).