Constantine the Emperorby David PotterOxford University Press, 2012It's no exaggeration to say, as the University of Michigan's David Potter does right at the beginning of his new book, that the Roman emperor Constantine "changed the world." No biographer of Constantine has refrained from saying this - indeed, the man's last English language biographer, Paul Stephenson, said it (in his Constantine: Roman Emperor, Christian Victor) just a couple of years ago. When Constantine publicly embraced Christianity on the eve of the Battle of the Milvian Bridge in 312, he not only reversed the brutal persecutions pursued by his imperial predecessors but gave Christianity the footing it needed to outstrip all its religious rivals. That did indeed change the world, and it's made Constantine irresistible to biographers ever since.Potter resists the hagiography that's tempted those biographers, but he doesn't resist it enough to hurt its feelings. His Constantine is a seeker as much as a cynic, tirelessly chasing his own ambitions but also chasing elusive (and interchangeable?) things like self-validation and a true God-experience. Readers who may have garnered the impression that Constantine was a hard-eyed pragmatic opportunist who very likely had no spiritual beliefs of any kind have come to the wrong shop. "For Constantine," Potter writes, "conversion was not the result of a sudden momentous revelation, but a journey over time and in his own mind."In any biography of Constantine, a great deal of scene-setting is necessary - despite the best efforts of two centuries of popularizers, the world of the Eastern Roman Empire remains baffling to most readers (Potter often inadvertently increases this problem in his attempts to avoid dry academic discourse; when he calls the Tetrarcy, the so-called college of four emperors, a "gang of four," it's hard to know how he expects it to help - readers who are old enough to remember Mao's little junta of the same name will be confused when they find no parallels here, for example). Potter does a very strong, very readable job of giving his readers a vivid feel for the strange world in which the young princeling Constantine grew up - a world that was knocked off its axis when the brutal, effective emperor Diocletian did the unprecedented and retired. As Potter notes, "Never before had a man at the height of his power voluntarily laid that power aside, exploiting the very symbols that he had made those of the imperial office." Potter is also adept at making good guesses as to the thoughts of his main characters (although he's a bit alarmingly cagey about them being guesses), as when he tries to put us in the mind of Diocletian's eventual successor:

Constantine's impression of that day would emerge over time. He would never build a retirement palace. He preferred to die in office. Retirement was one act of Diocletian's he could never hope to match.

We of course have no way of knowing what Constantine preferred or didn't prefer when it came to dying in office, but the contrast is interesting enough to let readers make the jump. Perhaps less so is his characterization of the climate of religious intolerance under Diocletian, which sounds positively idyllic:

Vicious as the rhetoric might be, and vicious as the conduct was on occasion, most people managed to get along most of the time. As the history of Diocletian's persecutions showed, most people preferred not to be drawn into violent quarrels with their neighbors; and if they felt their neighbors' religious practices were offensive, they were more likely to simply ignore them or refuse to associate with these people unless there was some external spark that might turn latent prejudice into violence.

Potter's research in this volume is obviously prodigious, yet his writing can often seem oddly hasty and unrevised. "Getting wind of Galerius' evil plan," he writes at one tense moment, "he [Constantine] rode like the wind through the night, pausing only to kill the post horses that might aid the pursuers he knew were behind him." Not only are a person's pursuers unlikely to be anywhere but behind him, and not only is the action suspect ("kill" is not the word Potter's source, Eusebius, uses to describe what Constantine does to his horses), but that giggle-inducing repetition of "wind" certainly looks accidental. In this and in a number of other places throughout, the text appears not to have been strictly edited at all, and the book's index is all but perfunctory  (increasingly common phenomena in the publishing world, although still rare for Oxford University Press).As in many scholarly volumes - even ones aimed at a general readership, as this one clearly is - one of the purest rewards for reading Constantine the Emperor comes at the very end: the author's end-notes are a vigorous, contentious walking tour through some of the controversies surrounding his subject and his sources. Readers are very naughty to skip end-notes just in general, but their loss would be compounded here.So: a volume that answers no crying necessity - amiable and authoritative, but lacking - as Stephenson's also did - that complicated spark of greatness that so unfailingly animated its subject. Constantine got a clear sign from the heavens that he would triumph; his biographers still await theirs.