The Battle of the Milvian Bridge was an unforeseen historical twist. Up to this time, the cross would to most people have been a symbol of shame. To the harassed and persecuted minority known as Christians, it represented God’s self-giving, peace-making sacrifice.

Churches in the West are hardly facing a return to the bad old days of being thrown to the lions or set alight to serve as torches in Emperor Nero’s gardens. But as their overt political and social influence declines – for better and for worse – internal debate over the proper relationship of Christians to the wider culture is intensifying.

For Constantine, by contrast, it appeared as a portent of military victory. One account of the battle reports that the emperor saw a cross of light in the sky, accompanied by a message: in this sign, conquer. Barely three centuries after Jesus’ death, soldiers fighting for the very empire that crucified him carried his sign into battle, painted on their shields.

From humility and determined non-violence to conquest: Constantine’s conversion story enacts in miniature the larger shift he would initiate as emperor, not only making this marginal religious movement legal but granting Christians their first real taste of power.

It’s become common – dare I say, fashionable? – for Christians today to look back on this turning point as the moment when the early church lost its way. It hopped into bed with the state, was seduced by power and influence, chose coercion over love and respectability over radical service. Only now, many feel, is the church finally getting back on track as a radical, dissident minority rather than a powerful political player.

Naturally, there’s some truth to this. But equally, the reality is always more complicated than the thumbnail version allows. Contrary to popular belief, Constantine (unlike later emperors) did not make his new faith the official religion of the empire, or force anyone to adopt it – the Edict of Milan in 313 simply granted full tolerance to Christianity, and to all other religions. It was normal for an emperor to promote his favourite god, and so the perks Constantine began to accord the churches were hardly surprising. They also made it possible for Christian communities to scale up some of their routine activities, such as the social welfare for which they were already known.

“Undoubtedly Christianity changed”, says Teresa Morgan, Professor of Graeco-Roman History at Oxford. “It became more establishment. It became more interested in money. It became more interested in protecting itself and its own prestige because of being allied with imperial power.

“On the other hand, it acquired opportunities to do what it saw as good, so I think it’s always a very two-edged thing, acquiring power – for any religious tradition, including early Christianity.”

These fateful first steps towards political dominance have a particular resonance for Christians today, as they watch the centuries-long project we now call Christendom recede ever further in the rear-view mirror.

Churches in the West are hardly facing a return to the bad old days of being thrown to the lions or set alight to serve as torches in Emperor Nero’s gardens. But as their overt political and social influence declines – for better and for worse – internal debate over the proper relationship of Christians to the wider culture is intensifying.

In infinitely more restricted circumstances than those facing the modern Western church, the early Christians found plenty of scope – not, of course, without cost – for doing the things they believed God had called them to do.

One question is how best to understand that culture. In biblical terms, this analysis is sometimes couched in terms of a more specific question: which city do we live in? Everyone agrees it’s not Jerusalem, the city of God – certainly not anymore. Lately, not so much Athens either, the (more or less) open marketplace of ideas. Babylon, then, the hostile overlords? Rome, the superpower demanding undivided allegiance?

Of course, whatever the results of the cultural analysis, the biblical response doesn’t change all that much. Paul in Athens engages respectfully with the prevailing culture. The prophet Jeremiah urges God’s people, exiled in hated Babylon, to “seek the peace and prosperity of the city to which I have carried you.”

And the early Christians in Rome, powerless, often excluded from civic life, periodically decimated by the murderous whims of the state? They served. They loved their neighbours. By the year 250, this embattled minority was supporting 1500 destitute people every day. When up to 5000 Romans were dying daily of one of the plagues that ravaged the ancient world in these centuries, Christians stayed when others fled and cared for the afflicted at risk to their own lives.

In infinitely more restricted circumstances than those facing the modern Western church, the early Christians found plenty of scope – not, of course, without cost – for doing the things they believed God had called them to do.

Commentators like Andrew Bolt take Christians to task for being “cowed” by the prospect of a new “war” on Christianity, and urge them to stand up and fight for their rights. The call to arms – to fight fire with fire – could hardly be further from the vibe of the New Testament. How can followers of Jesus set about ushering in the kingdom of God using ways and means that their King rejected outright?

Jesus insists over and over again that those who come after him will face fierce opposition. Panic is unbecoming to people who have been abundantly warned of what’s to come; the curious mix of humility and fearlessness displayed by those first Christians offers a better way forward.

Of course there are always complexities to be unravelled and addressed. But at the end of the day, the program for following Jesus in “post-Christian” Australia is unchanged: Keep Calm and Carry On Loving Thy Neighbour.

Natasha Moore is a Research Fellow at the Centre for Public Christianity. Visit www.publicchristianity.org