Inauguration of praefectus urbi in late antiquity

[Nathan Ross]

I'm writing a novel set in the fourth century AD

It would depend to an extent on what part of the 4th century you're writing about - the situation at the beginning would have been resolutely traditional, whereas by the end Christianity would have affected how things were done (albeit in ways that are hard to judge...)

Jerome (letter 23) describes what seems to be a consular inauguration ceremony in c.384; perhaps the ceremony for Vettius Praetextus, who actually died before taking up the post: "the consul... [was] in his triumphal robe... the highest dignitaries of the city walked before him as he ascended the ramparts of the capitol like a general celebrating a triumph; the Roman people leapt up to welcome and applaud him, and at the news of his death the whole city was moved."

This implies that the office holders of later Rome still held to many of the old pagan customs, and the ceremony for the praefectus urbi would perhaps have been similar - a procession through the city, headed by the chief magistrates, perhaps to the Capitol, with (if the man was a pagan) sacrifices at the major temples, and probably a public banquet. The most important thing, though, would probably be the games and shows the new magistrate was supposed to fund.

What form 'sacrifices' might have taken in the later empire is unclear. Constantinian legislation apparently outlawed public sacrifice, although other laws imply it might have been allowed in Rome itself at certain periods. If there were sacrifices, they would probably have been incense and wine rather than animal 'blood sacrifice'. Christian magistrates would have been on firmer ground with visits to churches!

Looking through the letters of Symmachus relating to the 'Altar of Victory' controversy might give you some useful pointers. Edward J Watts' The Final Pagan Generation focusses on the careers of Symmachus, Praetextus and others, but gives a good picture of the culture and political options of the Roman aristocracy in the 4th century, and the religious negotiations between the senatorial elite and the emperors. Neil Christie's From Constantine to Charlemagne: An Archaeology of Italy, AD 300-800 also has some useful stuff about the religion and politics of the city of Rome in late antiquity.

(Also, if you don't have it already, I'd recommend Michael Maas's Readings in Late Antiquity - nothing specific on inaugurations, but plenty of sources on the kind of ritualised acclamations and praises common in the later empire. The inscription from Aphrodisias gushily praising city patron Albinus (6th century) might be the sort of thing an incoming urban prefect of Rome would have heard!)