Dumbarton Rock is in the town of Dumbarton, west of Glasgow. The name "Dumbarton" comes from the Gaelic Dun Breatann, Fort of the Britons. Dumbarton Rock is mentioned by Monmouth as the site of one of Arthur's northern campaigns against the Picts and Scots. It is a large rocky peninsula with two peaks. The smaller peak at Dumbarton Rock was the one occupied in the Dark Ages, but the other peak has larger, recent ruins. The site overlooks the River Clyde, and you can almost see all the way to its mouth.
Dumbarton Rock has a long history of occupation and in fact, the rock was settled before the town of Dumbarton itself.. From the first century, during the late Roman and post-Roman eras, though Roman influence never reached this far west in Scotland. This region controlled the whole west of Scotland. Dumbarton Rock was a stronghold in the 5th and 6th centuries, the time of Arthur.
Excavation has revealed that earthwork ramparts defended Dumbarton Rock, and shards of Mediterranean amphorae pottery have been found. Part of ramparts had been torched and razed, perhaps in the Viking invasion of the Rock in 870.
The association of Dumbarton Rock with Arthur is less certain, though the place
is mentioned in passing in several of the legends. There is one legend that
associates Dumbarton Rock with Merlin,
though, who stayed for a time in the court of Rhydderych Hael, a ruler of Dumbarton.
Scottish Arthurian Sites