Known as "Archibald the Grim", he had been appointed Warden of the West March in 1361, and spent the following years attacking the English on both sides of the border. In 1372 he further gained the lands of the Earl of Wigtown, bringing all of Galloway under his control. In order to secure his new holdings, Archibald required a strong castle, and it is assumed that Threave Castle was built at this time. The main keep dates from this time, and was one of the first tower houses built in Scotland, standing alone without any outer defensive features. A harbour was formed to the west to provide access across the river. The excavations in the 1970s revealed remains of additional stone buildings, constructed in the late 14th century, which may represent a hall and a chapel.