Basilica, a code of law, drawn up in the Greek language, with a view to putting an end to the uncertainty which prevailed throughout the East Roman empire in the 9th century as to the authorized sources of law. This uncertainty had been brought about by the conflicting opinions of the jurists of the 6th century as to the proper interpretation to be given to the legislation of the emperor Justinian, from which had resulted a system of teaching which had deprived that legislation of all authority, and the imperial judges at last were at a loss to know by what rules of law they were to regulate their decisions. An endeavour had been made by the emperor Leo the Isaurian to remedy this evil, but his attempted reform of the law had been rather calculated to increase its uncertainty; and it was reserved for Basil the Macedonian to show himself worthy of the throne, which he had usurped, by purifying the administration of justice and once more reducing the law into an intelligible code. There has been considerable controversy as to the part which the emperor Basil took in framing the new code.

There is, however, no doubt that he abrogated in a formal manner the ancient laws, which had fallen into desuetude, and the more probable opinion would seem to be, that he caused a revision to be made of the ancient laws which were to continue in force, and divided them into forty books, and that this code of laws was subsequently enlarged and distributed into sixty books by his son Leo the Philosopher. A further revision of this code is stated to have been made by Constantine Porphyrogenitus, the son and successor of Leo, but this statement rests only on the authority of Theodorus Balsamon, a very learned canonist of the 12th century, who, in his preface to the Nomocanon of Patriarch Photius, cites passages from the Basilica which differ from the text of the code as revised by the emperor Leo. The weight of authority, however, is against any further revision of the code having been made after the formal revision which it underwent in the reign of the emperor Leo, who appointed a commission of jurists under the presidency of Sympathius, the captain of the body-guard, to revise the work of his father, to which he makes allusion in the first of his Novellae. This latter conclusion is the more probable from the circumstance, that the text of the code, as revised by the emperor Leo, agrees with the citations from the Basilica which occur in the works of Michael Psellus and Michael Attaliates, both of them high dignitaries of the court of Constantinople, who lived a century before Balsamon, and who are silent as to any second revision of the code having taken place in the reign of Constantine Porphyrogenitus, as well as with other citations from the Basilica, which are found in the writings of Mathaeus Blastares and of Constantine Harmenopulus, both of whom wrote shortly after Balsamon, and the latter of whom was far too learned a jurist and too accurate a lawyer to cite any but the official text of the code.

Authors are not agreed as to the origin of the term Basilica, by which the code of the emperor Leo is now distinguished. The code itself appears to have been originally entitled The Revision of the Ancient Laws (ἡ ἀνακάθαρσις τῶν παλαιῶν νόμων); next there came into use the title ἡ ἑξηκοντάβιβλος, derived from the division of the work into sixty books; and finally, before the conclusion of the 10th century, the code came to be designated ὁ βασιλικός, or τὰ βασιλικά, being elliptical forms of ὁ βασιλικὸς νόμος and τὰ βασιλικά νόμιμα, namely the Imperial Law or the Imperial Constitutions. This explanation of the term "Basilica" is more probable than the derivation of it from the name of the father of the emperor Leo, inasmuch as the Byzantine jurists of the 11th and 12th centuries ignored altogether the part which the emperor Basil had taken in initiating the legal reforms, which were completed by his son; besides the name of the father of the emperor Leo was written βασίλειος, from which substantive, according to the genius of the ancient Greek language, the adjective βασιλικός could not well be derived.

No perfect MS. has been preserved of the text of the Basilica, and the existence of any portion of the code seems to have been ignored by the jurists of western Europe, until the important bearing of it upon the study of the Roman law was brought to their attention by Viglius Zuichemus, in his preface to his edition of the Greek Paraphrase of Theophilus, published in 1533. A century, however, elapsed before an edition of the sixty books of the Basilica, as far as the MSS. then known to exist supplied materials, was published in seven volumes, by Charles Annibal Fabrot, under the patronage of Louis XIII. of France, who assigned an annual stipend of two thousand livres to the editor during its publication, and placed at his disposal the royal printing-press. This edition, although it was a great undertaking and a work of considerable merit, was a very imperfect representation of the original code. A newly-restored and far more complete text of the sixty books of the Basilica was published at Leipzig in six volumes (1833-1870), edited by K. W. E. Heimbach and G. E. Heimbach. It may seem strange that so important a body of law as the Basilica should not have come down to us in its integrity, but a letter has been preserved, which was addressed by Mark the patriarch of Alexandria to Theodoras Balsamon, from which it appears that copies of the Basilica were in the 12th century very scarce, as the patriarch was unable to procure a copy of the work.

The great bulk of the code was an obstacle to the multiplication of copies of it, whilst the necessity for them was in a great degree superseded by the publication from time to time of synopses and encheiridia of its contents, composed by the most eminent jurists, of which a very full account will be found in the Histoire au droit byzantin, by the advocate Mortreuil, published in Paris in 1846.