Looking north at Dumbarton Rock
chief fort of Strathclyde from the 6th century to 870. The fort of Alt Clut
was on the right-hand summit.
Dumbarton seen across the estuary of the River Clyde
at low tide.
Clach nam Breatann, Glen Falloch, perhaps the northern edge of Strathclyde
Ptolemy's Geographia – a sailors' chart, not an ethnographical survey – lists a number of tribes, or groups of tribes, in southern Scotland at around the time of the Roman invasion and the establishment of Roman Britain in the 1st century AD. As well as the Damnonii, Ptolemy lists the Otalini, whose capital appears to have been Traprain Law; to their west, the Selgovae in the Southern Uplands and, further west in Galloway, the Novantae. In addition, a group known as the Maeatae, probably in the area around Stirling, appear in later Roman records. The capital of the Damnonii is believed to have been at Carman, near Dumbarton, but around five miles inland from the River Clyde.
Although the northern frontier appears to have been Hadrian's Wall for most of the history of Roman Britain, the extent of Roman influence north of the Wall is obscure. Certainly, Roman forts existed north of the wall, and forts as far north as Cramond may have been in long-term occupation. Moreover, the formal frontier was three times moved further north. Twice it was advanced to the line of the Antonine Wall, at about the time when Hadrian's Wall was built and again under Septimius Severus, and once further north, beyond the river Tay, during Agricola's campaigns, although, each time, it was soon withdrawn. In addition to these contacts, Roman armies undertook punitive expeditions north of the frontiers. Northern natives also travelled south of the wall, to trade, to raid and to serve in the Roman army. Roman traders may have travelled north, and Roman subsidies, or bribes, were sent to useful tribes and leaders. The extent to which Roman Britain was romanised is debated, and if there are doubts about the areas under close Roman control, then there must be even more doubts over the degree to which the Damnonii were romanised.
The final period of Roman Britain saw an apparent increase in attacks by land and sea, the raiders including the Picts, Scotti and the mysterious Attacotti whose origins are not certain. These raids will have also targeted the tribes of southern Scotland. The supposed final withdrawal of Roman forces around 410 is unlikely to have been of military impact on the Damnonii, although the withdrawal of pay from the residual Wall garrison will have had a very considerable economic effect.
No historical source gives any firm information on the boundaries of the Kingdom of Strathclyde, but suggestions have been offered on the basis of place-names and topography. Near the north end of Loch Lomond, which can be reached by boat from the Clyde, lies Clach nam Breatann, the Rock of the Britains, which is thought to have gained its name as a marker at the northern limit of Alt Clut. The Campsie Fells and the marshes between Loch Lomond and Stirling may have represented another boundary. To the south, the kingdom extended some distance up the strath of the Clyde, and along the coast probably extended south towards Ayr.