In AD 312, Constantine one of four Roman emperors ruling a divided empire marched on Rome to establish his sole control of its western half. On the eve of the decisive battle he later claimed to have seen a 'Cross-shaped trophy of light' in the heavens, a sign that the Christian God was his patron, ensuring his victory. But Constantine's conversion was not a momentary revelation inspired by a vision. It was a lifelong process inspired by his own mother and aligned with radical developments in the later Roman world. During Constantine's lifetime, Christianity emerged from the shadows and under his rule, its adherents were no longer persecuted. Constantine the victorious general advanced a new triumphalist brand of Christianity, which became the empire's dominant faith and entrenched an institutional Church that could propagate and sustain the imperial religion.Constantine would go on to unite the eastern and western halves of the empire, establishing a new ceremonial stage, his eponymous victory city, Constantinople. This was not a new capital to replace Rome, nor was it an exclusively Christian construction. Yet it became the greatest Christian city in the world, the capital of Byzantium even as Rome itself fell to barbarian hordes.Paul Stephenson offers a nuanced and deeply satisfying account of a man whose cultural and spiritual renewal of the Roman empire gave birth to the idea of a unified Christian empire from which Europe would emerge. In Constantine: Unconquered Emperor, Christian Victor, a seminal figure in political and cultural history has found the biographer he deserves.