Based on previous research at the winter camp of the Viking Great Army at Torksey and Anglo-Scandinavian settlement at Cottam over 25 categories of metal artefacts are defined as diagnostic of Viking activity in Northumbria. Applying this model to over 15 sites, largely known only from metal-detecting, a common pattern is observed. At the majority, a large and fairly standardised Middle Anglo-Saxon finds assemblage is succeeded by just a few Viking finds, which we attribute to raiding following Halfdan's return to Northumbria with a portion of the Great Army in AD 876. At a smaller number of sites there are also assemblages of Anglo-Scandinavian finds, relating to the establishment of new settlements. The overall picture is of major settlement disruption and dislocation of existing land holdings in the late 9th century. This demonstrates, for the first time from archaeological evidence, the scale and impact of Viking activity in Northumbria.