Thule, a land believed by the ancient Greeks and Romans to be the farthest north in Europe. Its precise location was never determined. According to Roman writers, it was discovered and named by the Greek navigator Pytheas early in the fourth century B.C. Thule was supposedly an island where the sun did not set in midsummer. Later investigators believed that Pytheas' Thule was Iceland or the coast of Norway. In the first century A.D., the Roman general Agricola claimed to have sighted Thule as he sailed around Scotland. It is believed that he saw one of the Shetland or Orkney islands.

In time, Thule came to mean any distant region or, by extension, a difficult-to-achieve goal. The Romans added ultima (farthest) to the name. Ultima Thule or Thule is often used in the figurative sense in literature.