The Great Heathen Army:

But the Great Heathen Army paid a steep price for their smash-and-grab raids against the people of Mercia, one of the Anglo-Saxon kingdoms, whose king they forced into exile in Paris.

After marauding around the countryside, they were eventually beaten by Alfred the Great, King of Wessex, and agreed to peace and Christian baptism. But more than 250 of them ended up in a mass grave beside St. Wystan’s church in Repton, Derbyshire, then a major royal and religious centre of Mercia, in the winter of 874.