 There was a castle at Thurso East, which served as a residence of the earls of Orkney and Caithness, and it is probably the earthwork structure which was recorded in 1157 as the Thorsa castle.A fire gutted it in the early 16th century, and no vestige of it remains.The Arch, also known as Thurso Castle, was built in 1665 by George Sinclair, 6th Earl of Caithness.