(from Greek basilikos, “imperial”), 9th-century Byzantine (Byzantine Empire) code of law initiated by the emperor Basil I and completed after the accession of his son Leo VI the Wise.

The Justinian code of (Justinian, Code of) the 6th century, augmented by later imperial ordinances, had been the chief law source for the Roman world but was marred by much internal repetitiveness and inconsistency. Conflicting interpretations on how to select and apply elements of Justinian's works had contributed to uncertainty among imperial judges. Emperors Basil and Leo therefore had a commission of lawyers reexamine the code in order to abridge it, to cast out obsolescent, conflicting, and superfluous items, and to arrange the resultant provisions into orderly single titles. Basil's jurists apparently produced 40 books, which were enlarged to 60 under Leo.

The Basilica was written in Greek and was as much a collection of canon law as of civil and public law. It was far more systematically arranged than Justinian's code and comprised a single integrated work, unlike Justinian's four works, in which one subject might be treated in various places. The Basilica became the foundation of Byzantine jurisprudence.

In the 12th century an index for the Basilica was compiled. Because only about two-thirds of the Basilica survives, the index aids in rounding out knowledge of the contents. See also Justinian, Code of.