The great royal castle of Roxburgh, built by David I, was still held by the English. Situated on a hill above the junction of the Rivers Tweed and Teviot, near modern day Kelso, it seemed impregnable.

 During the night of Shrove Tuesday, 19th Feb 1314 Douglas and his men, in the dark of night, approached the castle on hands and knees covered in black cloaks in order to resemble the small black cattle of the period. Although seen from the battlements, the sentries remarked that the farmer must be drunk to allow his cattle to stray and risk having them stolen by the Black Douglas.

 Once under the walls rope ladders, that could be raised by means of inserting a spear tip into a socket at the top of the ladder and had been devised by one of Douglas's men called Sim of the Leadhouse, were hoisted into place. Although one sentry was alerted by the sound he was quickly silenced with a knife by the first man over the wall, thought to be Sim himself, Douglas being the second. The majority of the garrison were feasting in the great hall and were quickly dispatched.

 The commander, a Gascon, William de Fiennes managed to secure the great tower, however he was badly wounded in the face by an arrow and surrendered the castle on condition that he and his remaining men were free to leave for England. Following the pattern of denying fortifications to the enemy, Roxburgh's walls and towers were torn down.