Great works of art can be produced in barbarous societies - in fact the very narrowness of primitive society gives their ornamental art a peculiar concentration and vitality. At some time in the ninth century one could have looked down the Seine and seen the prow of a Viking ship coming up the river. Looked at today in the British Museum, it is a powerful work of art; but to the mother of a family trying to settle down in her little hut, it would have seemed less agreeable - as menacing to her civilisation as the periscope of a nuclear submarine.