Justinian I

In January 532 a riot that began in the hippodrome over the treatment of two condemned partisans turned into an insurrection that burned the centre of Constantinople and came close to putting another man on the throne. When it was over the cathedral was ash, and Justinian rebuilt it on a plan nothing in the Roman world had prepared anyone for.

The design was given to two men described as mechanikoi rather than as ordinary builders: Anthemius of Tralles, a mathematician who wrote on conic sections, and Isidore of Miletus, who taught geometry. Their solution set a shallow dome over a square by carrying it on four pendentives, curved triangles of masonry filling the corners, and then buttressed the whole thing east and west with half domes so that the interior reads as a single continuous space rather than a series of rooms. A ring of forty windows at the base of the dome makes the masonry above appear to float, an effect contemporaries wrote about at length. The church was dedicated in 537, less than six years after the fire.

It was not a solved problem. The first dome was too shallow, and it came down in 558 after earthquakes; the replacement was raised higher and has largely survived. The remark Justinian is supposed to have made at the dedication, that he had outdone Solomon, does not appear in the contemporary account by Procopius and is first found in a much later legendary narrative about the building, which is a useful reminder of how quickly a monument acquires the words it ought to have had.

Within months of his accession Justinian appointed a commission to sort out a thousand years of Roman legal material, and within six years it had produced the three works that carried Roman law into the European future: a code of imperial constitutions, the Digest, which condensed the writings of the classical jurists and discarded what the commissioners thought obsolete, and the Institutes, a students' textbook that has never entirely gone out of use. His own subsequent legislation was collected as the Novellae, and unlike the rest it was issued mainly in Greek, because that was the language his subjects actually spoke.

He legislated on belief with the same instrument. A law of 529 barred those who were not baptised from teaching, which ended public philosophical instruction at Athens and closed the last Neoplatonic school there; its head, Damascius, and several colleagues left for the Persian court and returned under the terms of a peace treaty a few years later. Whether the school reopened quietly afterwards is still argued from the archaeology of the Athenian houses. Repeated laws restricted Jews and Samaritans, regulated the Samaritan revolts brutally, and prescribed penalties for pagan sacrifice.

The doctrinal centrepiece was a failure on its own terms. Seeking to reconcile the miaphysite churches of Egypt and Syria without repudiating the Council of Chalcedon, he condemned three sets of writings known as the Three Chapters and forced the point through the Second Council of Constantinople in 553. The West resisted, Pope Vigilius was detained in the capital for years and changed his position more than once, and the eastern churches the policy was meant to win were not won.