Sailing up the Clyde towards Glasgow there is a vast and imposing sentinel guarding the river at Dumbarton. As a fortress Dumbarton Rock has a long and proud history, and, in fact, has a longer recorded history than any other in Britain.
The Kingdom of the Britons stretched along the River Clyde, north into Stirlingshire and south into Ayrshire. Dumbarton Rock, known as Dun Breatann - 'Fortress of the Britons' or 'Alt Clut' (Rock of the Clyde), was the stronghold of the Strathclyde Britons and a flourishing centre of a Britonnic culture that spoke Old Welsh, or Cumbric - a language now almost entirely forgotten.
Dumbarton Rock enters history in the mid 5th century with a letter of complaint from St Patrick to Coroticus, King of the Britons, telling him to stop kidnapping Christians and selling them into slavery.
A fascinating account of the Britonnic Scots is provided by Scotland's earliest poetry. 'The Gododdin', written by the Welsh bard Aneirin, tells the tale of a disastrous raid by the warband of the Britons of Edinburgh on the Angles, revelling in their deeds and mourning the loss of so many fine warriors.
By the mid 7th century only Dumbarton, of all the Britonnic Kingdoms of Scotland, had survived the Angles' onslaught. This has left us with the image of the Britons as doomed, heroic losers of the Dark Ages - an image depicted by their own poetry and their seemingly hopeless strategic position, trapped between the powerful Picts to the north and the Angles to the south. However, this is a mistaken image. The Britons were perfectly capable of defeating even the mightiest of their opponents.
For most of the 9th century Dumbarton seems to have avoided the worst of the Viking attacks which ravaged Scotland, that is until 866 AD, when Olaf the White, the Norse King of Dublin, brought a raiding army to plunder Scotland.
Olaf was married to Aud the Deep-minded, whose family controlled the Hebrides, and it seems likely that many Hebridean Vikings joined Olaf's army. For three years Olaf's army wreaked havoc, plundering and extorting money from Picts and Britons alike.
In 869 AD the Britons must have breathed a sigh of relief when Olaf returned to Ireland to curb Irish attacks on Viking Dublin. Never the less, Olaf swiftly returned to achieve one of his greatest feats.
Olaf and his brother Ivarr laid siege to the formidable rock fortress of Dumbarton. For four months the starving Britons held out, until the true death blow - the fortress's well dried up. At that point the Vikings broke in, plundering the kingdom of its treasures and taking a 'great host' of Britons to Ireland as slaves on a fleet of 200 ships.
The taking of Dumbarton was a terrific achievement: Olaf was famed in Icelandic Sagas as the "greatest warrior-king in the Western Sea". As was normal in the dark Ages, Olaf's luck didn't hold. Within a year he was dead, probably killed at the hands of Constantine I, King of Pictland.
For the Britons worse was to follow. Their king, Artgal, had escaped Dumbarton's destruction, perhaps fleeing to the seeming safety of Pictland; but there he too met his end, slain, it was said, 'on the counsel of Constantine'.
It was the end of the road for the Kingdom of Dumbarton but not for the Britons as a people. A new kingdom, further up the river, 'Strathclyde', would soon emerge.
It stretched along the Clyde valley and from Govan in Glasgow down to Penrith in Cumbria. Its royal centre was at Cadzow, near Hamilton, with Partick, in Glasgow, serving as a royal hunting forest.
In 878 the Britons may have gained revenge on the house of MacAlpin when Eochaid, son of Rhun, and his foster father, Giric, forced the house of MacAlpin from the Kingship of Pictland, however, in 889 they returned and expelled Giric and Eochaid.
For the Britons this may have been a disaster. The following year, Welsh sources note, the men of Strathclyde who didn't accept the new order, went into exile and settled in Gwynedd (or Wales). Following this exodus, Strathclyde seems to have become a sub-kingdom of the new Pictish and Gaelic Kingdom of Alba, with its royal line related to the Kings of Alba.
The last king of Strathclyde, Owein the Bald, died fighting for Malcolm II, King of Alba, at the Battle of Carham.