By the late middle ages and early modern era, the Greco-Roman Thule was often identified with the real Iceland or Greenland. Sometimes Ultima Thule was a Latin name for Greenland, when Thule was used for Iceland. By the late 19th century, however, Thule was frequently identified with Norway.
The Greek explorer Pytheas of Massalia (now Marseille, France) is the first to have written of Thule, after his travels between 330–320 BCE. Pytheas mentioned doing Thule in his now lost work, Things about the Ocean ὰ περὶ τοῦ Ὠκεανοῦ (ta peri tou Okeanou). He supposedly was sent out by the Greek city of Massalia to see where their trade goods were coming from. Descriptions of some of his discoveries have survived in the works of later, often skeptical, authors. Polybius in his Histories (c. 140 BC), Book XXXIV, cites Pytheas as one "who has led many people into error by saying that he traversed the whole of Britain on foot, giving the island a circumference of forty thousand stadia, and telling us also about Thule, those regions in which there was no longer any proper land nor sea nor air, but a sort of mixture of all three of the consistency of a jellyfish in which one can neither walk nor sail, holding everything together, so to speak."