Pytheas of Massalia (Πυθέας ὁ Μασσαλιώτης) was a Greek explorer, geographer, and astronomer from the colony of Massalia (modern Marseille) [1]. His voyage likely occurred in the late 4th century BCE, possibly after 323 BCE, when conditions allowed passage beyond the Strait of Gibraltar [1][2]. He sailed north along the Atlantic coast, reaching Britain ("Pretannike") and a distant land called Thule, which may have been Iceland, Norway, or the Shetlands [1][2][3]. Pytheas made early scientific observations on tides and described northern phenomena like the "congealed sea" [1][2].

His only known work is Περὶ τοῦ Ὠκεανοῦ (On the Ocean), a now-lost geographical and ethnographic account of his voyage in at least two books [1][2][4].

Pytheas provided the Mediterranean world with its first substantive information about northwestern Europe [1][2]. Though later authors like Strabo doubted him, his reports on Britain, tides, and the midnight sun were used by major geographers and remain a landmark in ancient exploration [1][2][4].

Sources 1. Stanford Encyclopedia of Philosophy (Stanford University): https://plato.stanford.edu/entries/pytheas/ 2. Encyclopædia Britannica (Encyclopædia Britannica, Inc.): https://www.britannica.com/biography/Pytheas 3. World History Encyclopedia (World History Foundation): https://www.worldhistory.org/Pytheas_of_Massalia/ 4. Oxford Research Encyclopedia of Classics (Oxford University Press): https://oxfordre.com/classics/view/10.1093/acrefore/9780199381135.001.0001/acrefore-9780199381135-e-5402