Diocletian

Diocletian's reforms were all aimed at one problem, that the empire had spent fifty years unable to keep an emperor alive, and the solution was to put the office out of reach. He divided rule between four men, two senior Augusti and two junior Caesars, and gave the two seniors divine patrons in their titles, Jovius for himself and Herculius for Maximian, so that the arrangement was presented as the order of heaven rather than as a committee. Access was ritualised: purple and jewels, elaborate ceremony, and the requirement that those admitted prostrate themselves and kiss the hem of the robe.

That is the setting for what came next. An emperor whose legitimacy rests on a visible and public relation to the gods has a practical interest in whether his subjects sacrifice, and the reign shows him acting on that interest before the church was touched at all. The rescript against the Manichaeans of 302 orders their books burned and their leaders punished, on the ground that a new sect arriving from Persia was corrupting a settled people with novelty. The reasoning is conservative rather than theological, and within a year the same reasoning was turned on the Christians.

The visual language matched the argument. Tetrarchic portraits stop showing individual faces and show instead four interchangeable rulers of one type, clasped together, and the porphyry group built into a corner of San Marco in Venice is the surviving example. An emperor who is a person can be killed and replaced. An emperor who is an office, held under a god whose name he carries, is harder to reach, and that was the point of every part of the design.

The edicts began in 303 and escalated. First the destruction of church buildings and the surrender of scriptures, then the arrest of clergy, then their release on condition of sacrifice, and finally, in 304, a general order that everybody sacrifice. Enforcement varied enormously by region and by the appetite of the local ruler, which is why the persecution was severe in the east and in Africa and slight in the west. Galerius called it off in 311 in an edict that effectively admitted it had not worked, and Constantine reversed the policy outright soon afterwards.

Two consequences outlasted the empire in the west. The first is a quarrel. Clergy who had handed over the scriptures were called traditores, and in North Africa the question of whether sacraments administered by such men were valid produced the Donatist schism, which was still running a century later and drew Augustine into some of his most consequential writing about what a church is. The second is a calendar. The Coptic Orthodox Church counts its years as the Era of the Martyrs, and the epoch it dates from is the accession of Diocletian. A church that survived him keeps his name at the head of every date it writes, which is a stranger memorial than anything he built.