This work is essentially a 4346-line poem from the middle English period. As the name suggests, it is "alliterative" and is a retelling of the legend of King Arthur. This work has been dated from about 1400; in terms of documentation most interesting thing about it is that it is preserved just in the Lincoln Thornton manuscript.
The author of the poem is unknown, not unlike some if the works of that time. However, there has been a mention of a Scottish poet Huchoun. However, there is a serious argument against his authorship due to the conflict between his native dialect and that of the work.
The Alliterative Morte Arthure is considered a relatively realistic depiction of the events of the legend. It is also interesting that despite having a romantic subject, this work isn't that much of a romance. Due to this realism, Arthur is less of a glorified being and more of a flawed character.