Early Medieval literature was not written. It is was passed by word of mouth from one generation to another by English, Welsh, Scottish and Irish Medieval Bards. The origins of the stories about King Arthur and the Arthurian Legend are found in many Welsh legends and Celtic Myths which were told by the Medieval Bards.

The Medieval bards were a distinct class with hereditary privileges. They appear to have been divided into three great sections: the first celebrated victories and sang hymns of praise; the second chanted the laws of the nation; the third gave poetic genealogies and family histories.  http://underwatergunfight.tumblr.com/page/57