Thule was a northern kingdom of the pre-Cataclysmic period. Originally the prehuman civilisation of Ultima Thule was inhabited by the pre-human ancestors and the Voormi, before being colonised by survivors from Zobna. Thule was overwhelmed by the same ice-sheet which destroyed Hyperborea. Survivors from Thule founded an new colony in the northern part of the Thurian Continent until the ice-sheet retreated, when some of them returned to the island. Thule or Thoule was reported in the 4th century B.C. by the Greek explorer Pytheas of Massilia, identified variously with the Orkney and Shetland Islands.
Thule is a real "lost land" which has been absorbed into the Mythos by various hands, including Robert E. Howard and Clark Ashton Smith. Lin Carter, as part of his systemizing, has tied the various references together into the current version.