In the countryside of England’s East Midlands, less than a mile from the house where I spent my childhood, there is a small, wooded area named Hunsbury Hill. The actual hill, as I remember it, is a slight thing among the trees: its top flattened off and surrounded by a circular ditch eight or ten feet deep. Back in those days when kids were let loose to find their own fun, it was a popular play spot for us urchins from the nearby public housing estate. Local people never said “Hunsbury Hill.” They called the place “Danes’ Camp” because Viking...