Alt Clut (fortress)

Dumbarton Castle
Dumbarton, Scotland GB grid reference NT250734
View of Dumbarton Castle from across the River Clyde
Dumbarton Castle
Coordinates	55°56′10″N 4°33′46″W / 55.9360°N 4.5628°W / 55.9360; -4.5628
Site information
Owner	Scottish Government
Controlled by	Historic Environment Scotland
Open to the public	Yes
Site history
Built	Site occupied since the Iron Age
In use	Still in use today

Dumbarton Castle (Scottish Gaelic: Dùn Breatainn, pronounced [d̪̊unˈb̊ɾʲɛhd̪̊ɪɲ]) has the longest recorded history of any stronghold in Scotland. It overlooks the Scottish town of Dumbarton, and sits on a plug of volcanic basalt known as Dumbarton Rock which is 240 feet (73 m) high.

According to the local museum, Dumbarton Rock is a volcanic plug of basalt created 334 million years ago, with the softer exterior of the volcano having weathered away.

At least as far back as the Iron Age, this has been the site of a strategically important settlement. Its early residents were known to have traded with the Romans. The presence of a settlement is first recorded in a letter Saint Patrick wrote to King Ceretic of Alt Clut in the late 5th century.

David Nash Ford has proposed that Dumbarton was the Cair Brithon ("Fort of the Britons") listed by Nennius among the 28 cities of Sub-Roman Britain. From the fifth century until the ninth, the castle was the centre of the independent Brythonic Kingdom of Strathclyde. Alt Clut or Alcluith (Scottish Gaelic: Alt Chluaidh, pronounced [aɫ̪d̪̊ˈxɫ̪uəj], lit. "Rock of the Clyde"), the Brythonic name for Dumbarton Rock, became a metonym for kingdom. The king of Dumbarton in about AD 570 was Riderch Hael, who features in Welsh and Latin works.