Historians like a quiet life, and usually they get it. For the most part, history moves at a deliberate pace, working its changes subtly and incrementally. Nations and their institutions harden into shape or crumble away like sediment carried by the flow of a sluggish river. English history in particular seems the work of a temperate community, seldom shaken by convulsions. But there are moments when history is unsubtle; when change arrives in a violent rush, decisive, bloody, traumatic; as a truck-load of trouble, wiping out everything that gives a culture its bearings - custom, language, law, loyalty. 1066 was one of those moments.