Perhaps Here Too

We should be startled if we were quietly reading a prosaic modern novel, and somewhere in the middle it turned without warning into a fairy tale. We should be surprised if one of the spinsters in Cranford, after tidily sweeping the room with a broom, were to fly away on a broomstick. Our attention would be arrested if one of Jane Austen's young ladies who had just met a dragoon were to walk a little further and meet a dragon. Yet something very like this extraordinary transition takes place in British history at the end of the purely Roman period. We have to do with rational and almost mechanical accounts of encampment and engineering, of a busy bureaucracy and occasional frontier wars, quite modern in their efficiency and inefficiency; and then all of a sudden we are reading of wandering bells and wizard lances, of wars against men as tall as trees or as short as toadstools. The soldier of civilization is no longer fighting with Goths but with goblins; the land becomes a labyrinth of faërie towns unknown to history; and scholars can suggest but cannot explain how a Roman ruler or a Welsh chieftain towers up in the twilight as the awful and unbegotten Arthur. The scientific age comes first and the mythological age after it. 

From Chesterton's A Short History of England.