The Arthurian period spans the years between Arthur's father, Uther Pendragon during the late 5th century and the naming of a subsequent king, Maelgyn of Gwynedd circa AD 542.

So, who ruled in between?

Uther, brother of Ambrosius Aurelianus, was overall king of the Britons, with many other kings and sub-kings of various tribal districts all fighting against the invading Saxons and Angles from the east.

There are various historical references to a 'King Arthur', notably Nennius, an early 8th century Celtic monk who wrote that Arthur, the leader of the Britons, fought one of his battles on Badon Hill, probably Solsbury Hill near Bath. This battle is generally dated to 495, but could have been much later.
Nennius, together with a later manuscript (Bonedd Y Saint) confirms that Ossa, king of the English, fought against Arthur at Badon and died during the siege.

The historian and monk, Gildas, who was the first to mention Badon, wrote in the 540's (the age of the saints) that the battle was a siege but does not say who besieged who, nor mentions any names. It matters not, because the outcome was decisive, albeit not mentioned in the Anglo-Saxon Chronicle. Gildas, in his critical sermon, named Maelgwn (with whom he was contemporary) as one of the British tyrants.

The Anglo-Saxon Chronicle is ambiguous on the names of Hengest, his son, Ochta and grandson, Ossa, although King Ossa is known to have ruled from Kent for a long period before his expedition east to confront the Britons at Badon.

So, although Arthur is not mentioned as a king or leader in any of the genealogies it seems certain that he was, indeed, the hero of the Britons for over 40 years. Although mentioned in some early Welsh sources such as The Mabinogion, (partly 11th century), Arthur was largely forgotten until Geoffrey of Monmouth wrote his History of the Kings of Britain in 1135. Geoffrey was not responsible for the far-fetched romance stories which were invented later by others.

This leaves us with one question – where did Arthur come from? The early Welsh genealogies, together with Geoffrey tell us that Uther Pendragon and his brother Ambrosius were sons of Constantine the Cornovian - murdered circa 443 - who was related through a supposed family bloodline to Constantine the Great. Constantine the Great was declared Roman emperor at York on the sudden death of his father, Constantius, in 306.

A concentrated study of the early Celtic genealogies and the Book of Llandaff leads us to Meurig 1, king of the old Silurian territory during the second half of the 5th century (not to be confused with King Meurig 11, who ruled during the latter part of the 6th century). Meurig 1 is well attested as the King of Gwent and Erging during the 5th century and is the only person to equate with the pendragon's floruit.

This theory firmly places his son Arthur as of Roman bloodline and raised in south-east Wales. Indeed, just as postulated by Geoffrey of Monmouth.