Pytheas (flourished 300bc,Massalia, Gaul) was a navigator, geographer, astronomer, and the first Greek to visit and describe theBritish Isles and the Atlantic coast of Europe. Though his principal work,On the Ocean, is lost, something is known of hisventures through the Greek historianPolybius (c. 200–c. 118bc).

Sailing from theMediterranean Sea into the Atlantic, Pytheas stopped at the Phoenician city of Gades (present-day Cádiz, Spain), probably followed the European shoreline to the tip of Brittany, and eventually reached Belerium (Land’s End, Cornwall), where he visited the tin mines, famous in the ancient world. He claimed to have explored a large part ofBritain on foot; he accurately estimated its circumference at 4,000 miles (6,400 km). He also estimated the distance from north Britain to Massalia (Marseille) at 1,050 miles (1,690 km); the actual distance is 1,120 miles (1,800 km). He visited some northern European countries and may have reached the mouth of theVistula River on theBaltic Sea. He also told ofThule, the northernmost inhabited island, six days’ sail from northern Britain and extending at least to theArctic Circle; the region he visited may have beenIceland orNorway.

His comments on small points—e.g., on the native drinks made of cereals and honey and the use of threshing barns (contrasted with open-air threshing in Mediterranean regions)—showacute observation. His scientific interests appear from his calculations made with a sundial at thesummer solstice and from notes on the lengthening days as he traveled northward. He also observed that the polestar is not at the true pole and that the Moon affects tides.

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