the dark ages (yes an anglocentric term) are so called for the distinct lack of documentation on the period. its also disputed and in my opinion misinterpreted that the term applies to the paganism in northern europe during the period. whilst this is partly true i think the term is best seen as describing a period of turbulence between the gradual decline of roman influence in the region and the new era of norman overlordship typically beginning with the definitive victory over the anglo-saxons at hastings in 1066. i suppose, as a result, the dark ages is really a nominal term for the specific period of time in which the anglo-saxons and danes jointly dominated britain prior to the norman conquest.