For travellers disembarking at Ravenna’s modest railway station from, say, Venice or Rome, the idea that this unassuming town was once the ‘crucible of Europe’ might seem an extravagant assertion, lent only a vague veneer of credibility by an afternoon wandering between the stubby bulk of the mausoleum of Theoderic and the golden mosaics of Emperor Justinian I and his wife, Theodora, in the church of San Vitale. Yet Judith Herrin’s Ravenna both makes this claim and performs the seemingly impossible task of rescuing its subject from obscurity, charting an improbable journey from marsh-enfolded outpost to imperial capital and cultural dynamo.

To do so involves navigating a complex course through the centuries when the Western Roman Empire was collapsing and a new world of Germanic monarchs, ecclesiastical potentates and Byzantine emperors was beginning to replace it. Ravenna, as Herrin skilfully reveals, lay at a critical spot, where these forces mingled. It