Dumbarton Rock has been fortified for over 1500 years, and is first recorded in the 5th century as the fort of Alcluith, seat of Ceretic, the British King of Strathclyde.
Having previously been the capital of the independent Kingdom of Strathclyde, in 1018 it was absorbed into Scotland by Malcolm II, and by 1222 a castle had been built on it.
Dumbarton Castle was an important site from the 13th century through to the end of the 16th century, but from the the mid-17th century its importance declined.
The majority of the castle today dates from the 18th century, when the castle was refortified, probably against perceived threats from the Jacobites and the French. Little remains of the older castle, although there is the Portcullis Arch, dating back to the 14th-century, the lower course of the Wallace Tower (supposedly named for William Wallace after he was held prisoner here), and a guard house dating to around 1580.