At the beginning of the 5th century the Roman governor of Britain gathered together all the legions in Briton and, within two weeks, left to try and become Emperor. He failed and the legions never returned to Britain. This left Britain exposed to the constant menace of the Picts, Irish and Germans (mainly the Angles, Saxons and Jults who, along with the Normans and Vikings, form the modern English). The British leaders wrote to the Emperor about the defences of Britain in 410 AD. The Emperor told them to look after their own defences. This they did and they appointed a High King in 425 AD. A Roman way of life remained in Britain for 2 or 3 generations. Roman titles and practices where kept by the ruling classes of the Britons. However, the High King used a Celtic title, Vortigern(?), which implied that he took support from all sections of the population.
The invaders kept coming and some of the town and cities in Briton where destroyed or taken over. The High King invited two Jultish leaders to form a mercenary army to help him. In return he gave them land in Kent. This was a common practice at the later end of the west Roman Empire. These Jults brought more supporters from Jultland (modern day Denmark) and in 441 AD they revolted in a very bloody revolt. The Germans had a very strong foot hold in Briton and began to push the Britons westward. The High King had let the invaders in by the back door! The fighting continued on and off into the next century and this was the violent times that gave rise to a British general who later became known as King Arthur!
There is not much mentioned about Arthur from the end of the 5th century and the beginning of the 6th century which is about the time he lived. The first mention of him comes in a Welsh poem, Y Gododdin . The poem records the exploits of a band of worriers who set out from Edinburg to do battle with the German invaders. They defeated the Germans but where wiped out themselves. The poem said that it was a great victory despite the fact there leader was not as good as Arthur! In 540 AD a monk called Gildas wrote a damming account of the state of Britain at that time in a book called Concerning the Ruin of Britain (De Excidio Britanniae). He considered that it was due to the immoral behaviour of the British war lords who spent much of their time fighting amongst themselves. In this account Gildas gives great details of the 6th century but he does not mention Arthur. This along with the lack of other evidence has suggested to some historians that Arthur was not a real person. However, from this time onwards the name Arthur is given to boys but the name was never used before the 6th century. This suggests that there was a person of that name that people wished to name their sons after. If there was no Arthur than another character will be need to explain the defeat of the Germans in the 6th century. One possible explanations for Gildas not mentioning Arthur is because Arthur is not a real name as such (it possibly comes from a Roman name Artorus(?)). It was possibly a title in the same way that Caesar was a name that was later used as a title. Now Guildus does mention a British general called Ambrosias(?) who did much the same things as Arthur. It could be that Ambrosias and Arthur are one and the same person with Ambrosias as his name and Arthur as his title. Another possible explanation lies in the fact that Guildus did not mention other people and events that where important at the time so missing out Arthur may have no significance. Yet another theory is that Arthur followed on from Ambrosias and, therefore, was not around in 540 AD.
The first major writing on Arthur is in "The History of the Britons". This was a compilation of writings that were collected by a monk called Nennius and was published in 829 AD. It mentions Arthur and calls him Miles which is Latin for solder or knight. Nennius was Welsh and in his book he gives an account of the battles that Arthur fought and won describing him as the commander for all the battles. The battle at Mons Badonicus (Badon Hill) resulted in the overwhelming defeat of the Germans. The German army at that battle was made up of Jults, Angles and Saxons from England and as much worriers as they could get from their German home lands. It was lead by a man called Ale. This defeat meant that they did not return for about 40 - 50 years. The Britons spent that time fighting amongst themselves. Nennius says that Arthur and his son where killed in a power struggle at the battle of Camlan, they where on opposing sides.
After that other poems about Arthur added to the tales. The Holy Grail (from a poem about Percivale), Knights of the Round Table and the Sword in the Stone (Roman de Brut by Layamon) where all added by the time we get to 1136 when Geoffrey of Monmouth, another Welsh monk, wrote "The History of the kings of England" (Historia Regum Britanniae). Geoffrey was an Arthur fanatic. He joined the church to further his writing ambitions and his book was written more to entertain than to give an accurate historical account. However, it was wildly believed at the time to be a true record of the history of Britain. The events added to the Arthur tales possible come from other legends and myths that had been passed down in the oral tradition of the Celtic people. One thing that Geoffrey did that others had not was to call Arthur a King.
This all set the stage for the Morte d'Arthur by Sir Thomas Malory in 1485 which is THE King Arthur story that we know today. In this book Arthur is transformed from a Romo-British general who battled agenst the invading Germans who would eventually become the English into the model of a English King! The book was written as political propaganda and to reinforce the feudal society in England.
Arthur was a real person. He commanded a well organised and disciplined army that was highly mobile consisting of mainly horsemen. It was well equipped and it defeated a large, fanatic army of Germans. Most of the other people in the Arthur legends where also real - Merlin, Guinevere, Lancelot (who was borrowed, by Chrétien de Troyes, from a French legend and never lived in England) - but some of the charters where false.