It became a royal castle, and in the 16th century hereditary responsibility for Threave was given to the Lords Maxwell. It was briefly held by the English in the 1540s, but did not see serious action until the Bishops' Wars, when in 1640 a royalist garrison was besieged by a force of Covenanters. Partially dismantled, the castle remained largely unused until given into state care in 1913. The ruins, comprising the substantially complete tower house and the L-shaped artillery house, are today maintained by Historic Environment Scotland as a scheduled monument.