Three millenniums ago, a small farming community briefly flourished in the freshwater marshes of eastern England. The inhabitants lived in a clutch of thatched roundhouses built on wooden stilts above a channel of the River Nene, which empties into the North Sea. They wore clothes of fine flax linen, bartered for glass and amber beads imported from places far-flung as present-day Iran; drank from delicate clay poppyhead cups; dined