Siege of Dumbarton

The siege of Dumbarton was a successful four-month siege of the Brittonic fortress at Dumbarton Rock in 870, initiated by the Viking leaders Amlaíb, King of Dublin, and Ímar. Dumbarton was capital of the Kingdom of Alt Clut, the only surviving Brittonic kingdom outside of Wales. It represented a valuable target for the Viking invaders, who were likely motivated by strategic considerations, as well as loot. The attackers may have wished to remove Alt Clut as a maritime power, and the location and defensiveness of Dumbarton itself was of major value. The siege lasted four-months, a length of time unprecedented in the history of Viking warfare in the British Isles, and ended when the defenders ran out of water. After the siege numerous prisoners were taken and sold into slavery in Dublin. Following this defeat, the power centre of Alt Clut moved to the vicinity of Govan, and it became known as the Kingdom of Strathclyde. The loss of Dumbarton caused the kingdom to increasingly fall under the influence of the Scottish Kingdom of Alba.