A flat 8-ha (20-acre) island on the River Dee in Dumfries and Galloway, Threave lies a mile (1.5 km) to the west of Castle Douglas. Threave Castle was erected here by Archibald the Grim shortly after he was created Lord of Galloway by King David II in 1369. Recent archaeological investigations have located the remains of a mediaeval riverside harbour which served the castle.