The present state of archaeological research suggests that there was something akin to a Dark Age in Ireland during the centuries before Christian conversion. This period – from the first century (bc) to the fourth century (ad) – may, for convenience, be called the Late Iron Age. It coincided, for the most part, with the Roman Empire: its beginning came as Roman power was being extended further into Gaul and it came to an end in the late Empire, when imperial frontiers were under attack by, among others, the Irish. A problem is posed, ther efore, by this chronology: was the coincidence between Roman power and this Irish Dark Age a mere coincidence, so that a low ebb of farming activity and artefactual output just happened to endure while Roman power in north-western Europe was at its peak? Since this history of Early Christian Ireland takes its starting-point from the beginning of organised Christian missionary activity in Ireland, the crucial aspect of this problem is a more particular question: why was it that an economic revival and a vastly increased impact of Roman civilisation occurred when the power of Rome in north-western Europe was in terminal decline? Yet, although this latter question alone is directly relevant, it may perhaps only be answered as part of the larger problem about the relationship of Ireland and Rome.