When Roman power faded from Britain in the fifth century, the Britons of the Clyde — descendants of the Damnonii — emerged as a kingdom of their own. Its ancient name was Alt Clut, ‘the Rock of the Clyde’: Dumbarton Rock, the twin-peaked volcanic plug rising sheer from the river a dozen miles below Glasgow, one of the longest-inhabited fortified places in Britain. From it a line of kings ruled the valley for centuries, speaking Cumbric — a Brittonic tongue closer to Welsh than to anything spoken in Scotland today — and it is in their world that tradition sets St Mungo, patronised by the Strathclyde king Rhydderch Hael.
Alt Clut held its own in the violent politics of early Britain — against Picts, Angles of Northumbria and the Gaelic Scots of the west — until catastrophe came from the sea. In 870 the Viking kings Olaf and Ivar brought a great fleet up the Clyde and besieged Dumbarton Rock for four months until its well failed; the fortress fell, and the following year the victors carried a vast train of captives back to Dublin for the slave markets. It is among the darkest recorded events ever to happen on this river.
The kingdom survived the blow, but changed. Its centre of gravity moved upriver, to the heart of what is now Glasgow’s south side: a royal estate at Partick and, facing it across the river, the great church site of Govan. There the kings of what was now called Strathclyde — ‘the valley of the Clyde’ — buried and commemorated their dead in spectacular style. The Govan Stones, preserved today in Govan Old Parish Church, are one of Britain’s great early medieval collections: a magnificent carved sarcophagus, crosses, and the largest group of Viking-age ‘hogback’ monuments anywhere — the treasury of a lost kingdom, sitting quietly amid the tenements and the shipyard gates.
Strathclyde’s end came not with another siege but by absorption. Through the tenth and eleventh centuries the expanding Gaelic kingdom of Alba drew Strathclyde into its orbit — sometimes ally, sometimes prey, latterly a sub-kingdom for heirs to the Scottish throne — until, by the early eleventh century, its last native kings disappear from the record and the Clyde valley passed finally into the kingdom of the Scots. Cumbric faded from its valleys, surviving only in place-names: Glasgow, Partick, Govan and dozens more are words of Strathclyde.
Glasgow is that kingdom’s child. The city’s site, its saint, its name and its oldest neighbours all come out of Strathclyde — and when the medieval bishops later built their cathedral over Mungo’s tomb, they were consciously reviving the holy place of the old British kingdom. Its story is told in stone three miles apart: on Dumbarton Rock, and among the Govan Stones.