In the book King Arthur:a military history by Michael Holmes (1996), the author attempts to lay out the potential role a hypothetical Arthur could have played in military events around the Romanized Britons attempted defense of Britain against the Anglo-Saxon invaders.
The book is divided into chapters focusing upon a number of topics. The author touches upon the question of the historical authenticity of King Arthur in the first chapter, then moves on to discuss what is known of the Roman and Celtic influences and writings about Arthur’s alleged existence.
The next chapters are an attempt to define the state of the 5th century military situation in Britain, as the Anglo, Saxons, and Jutes pushed further into the island from the east. Holmes reviews the various primary sources of writing we have of this time, and tries to construct a logical, and likely pattern of events from the initial invasion from a potential Saxon mercenary army invited into the island by the the shadowy historical figure Vortimer, as part of an internal despite among the Roman Britons. Then he discusses the likely betrayal by the Saxons of their Celtic employers. This is followed by a speculative campaign by Ambrosius Aurelianus, the likely British High King, against the invaders.
Holmes then speculates that the niche where a historical Arthur would fill would be in conducting the field campaigns of unified Britons against the invaders after or during the late years of Ambrosius’ reign. All of this is put together with deductive logic, scant primary sources, and a bit of speculation.
The author compares the Germanic conquest of Britain with the Germanic conquest of Gaul by the Franks. After the death of Flavius Aetius, the General of the West, Roman Gaul would stay an uneasy balance between Roman and early migrating Germanic tribes. In two generations the Frankish king Clovis would take power and quickly conquer most of what was left of the Roman province against the Goths and what was left of the Roman forces, within 30 years establishing a kingdom that spanned much of modern day France.
In Britain the Anglo-Saxon invasion would experience many more setbacks. By 500 A.C.E., the invaders controlled Kent, Lincoln shire, Norfolk, Suffolk, the Isle of Wight, and coastal areas in Northumberland and Yorkshire. The back and forth fighting between the Britons and invaders would depopulate cities and lay waste most of the farm steads between the conflicted territory.
Holmes is proposing that Arthur lead a serious of campaigns against the Saxons, climaxing in the Battle of Baden, and it was these hypothetical campaigns which checked the invaders for a several decades. Such battles are known to have existed, but the primary sources are very sparse on the details of when and where these clashes were conducted.
As a work of historical speculation it is a good read. Holmes has keep the work to about 180 pages, with proper notations of his sources. Then book is worth a read for anyone interested in the historical authenticity of Arthur, or even the Anglo-Saxon invasions of Britain.