The Picts are commonly described today as a group of tribes and/or independent kingdoms who lived in the eastern and northeastern regions of Scotland during the ancient and early medieval period (from 600 BCE through 900 CE). The Picts occupied an area in Scotland that ran approximately from the Firth of Forth in the south to Shetland Island in the north. Included in this area is Orkney, an archipelago in northeastern Scotland. (http://www.dailykos.com/story/2016/6/19/1540134/-Ancient-Orkney-The-Picts-P...)

"Then it was, that the magnanimous Arthur, with all the kings and military force of Britain, fought against the Saxons. And though there were many more noble than himself, yet he was twelve times chosen their commander, and was as often conqueror. The first battle was in the mouth of the river which is called Glein. The second and third and fourth and fifth on another river which is called Dubglas and is in the region Linnuis. The sixth battle on the river which is called Bassas. The seventh battle was in the forest of Celidon, that is Cat Coit Celidon. The eighth battle was near the fort Guinnion, where Arthur bore the image of the Holy Virgin, mother of God, upon his shoulders, and through the power of our Lord Jesus Christ, and the holy Mary, put the Saxons to flight, and pursued them whole day with great slaughter. The ninth battle was fought in the city of the Legion. He fought the tenth battle on the shore of the river called Tribruit. The eleventh battle was fought on the hill called Agned. The twelfth was a most severe contest, when Arthur penetrated to the hill of Badon. In this engagement, nine hundred and forty fell by his hand alone, no one but the Lord affording him assistance. In all these engagements the Britons were successful."

"The Historia Brittonum is thought to originate sometime during the ninth century but the oldest surviving copy is in BL MS Harley 3859 (also known as Epitome rei militaris), which dates from the first half of the twelfth century. Scholars are unsure how much of the text handed down to us in this manuscript is true to the ninth-century original, and how much was changed by the author of this recension (previously thought to be Nennius, now referred to on the whole as Pseudo-Nennius due to uncertainty surrounding this attribution), who may have been influenced by eleventh and twelfth-century Welsh Arthurian tradition. Conversely, this text may have influenced other contemporary twelfth-century writers of Arthuriana – Geoffrey of Monmouth’s Historia Regum Britannia shares several similar features and plot devices with our Historia." (https://medievalbex.wordpress.com/2012/12/05/the-arthurian-tradition-histor...)