Much of what is known about Pytheas comes from commentary written by historians during the classical period hundreds of years after Pytheas's journeys occurred,[5] most familiarly in Strabo's Geographica (late 1st century BC, or early 1st century AD),[6] passages in the world history written by Diodorus of Sicily between 60 and 30 BC, and Pliny's Natural History (AD 77).

The last link was supplied by Strabo, who said that an emporium on the island of Corbulo in the mouth of the river Loire was associated with the Britain of Pytheas by Polybius.

[18] Because there are scant first-hand sources available regarding Pytheas's journey, historians have looked at the etymology for clues about the route he took up the north Atlantic.

[citation needed] Diodorus Siculus gave a similar number:[19] 42,500 stadia, about 4,830 miles (7,770 km), and explains that it is the perimeter of a triangle around Britain.

The earliest existing records of the word are quotations of the periplus by later authors, such as those within Strabo's Geographica, Pliny's Natural History and Diodorus of Sicily's Bibliotheca historica.

[23] According to Strabo, Pytheas referred to Britain as Bretannikē, which shares more similarities with spellings in the modern Celtic languages than its Classical Latin variants.

Furthermore, some proto-Celtic was spoken over all of Greater Britain, and this particular spelling is prototypical of those more populous regions, but there is no evidence that Pytheas distinguished between the peoples of the archipelago.

The first written reference to Scotland was in 320 BC by Pytheas, who called the northern tip of Britain "Orcas", the source of the name of the Orkney islands.

[32][33] Strabo, taking his text from Polybius, related that "Pytheas asserts that he explored in person the whole northern region of Europe as far as the ends of the world.

[37] Pliny added that it had no nights at midsummer when the sun was passing through the sign of the Crab (at the summer solstice),[8] a reaffirmation that it is on the Arctic Circle.

If Berrice was in the outer Hebrides, the crossing would have brought Pytheas to the coast of Møre og Romsdal or Trøndelag, Norway, explaining how he managed to miss the Skagerrak.

From the time of the Roman Empire all the possibilities were suggested repeatedly by each generation of writers: Iceland, Shetland, the Faroe Islands, Norway and later Greenland.

The fact that Pytheas lived centuries before the colonization of Iceland and Greenland by European agriculturalists makes them less likely candidates, as he stated that Thule was populated and its soil was tilled.

What he seems to be describing is an agricultural country that used barns for threshing grain rather than the Mediterranean outside floor of sun-baked mud and manufactured a drink, possibly mead.

[47] William Ogle, a major translator and annotator of Aristotle, attributes the name sea-lung to the lung-like expansion and contraction of the Medusae, a kind of Cnidaria, during locomotion.

According to The Natural History by Pliny the Elder:[11]Pytheas* speaks of an estuary of the Ocean named Metuonis and extending for 750 miles, the shores of which are inhabited by a German tribe, the Guiones.

Philemon denies the suggestion that amber gives off a flame.The "Guiones" who Pliny places in Germania (and not Scythia), are sometimes reinterpreted by modern editors to be Gutones, who are in turn generally seen as predecessors of the later Goths.

This raises doubts about the reliability of Pliny's interpretation of older geographers of this region, but it also makes it clear that Pytheas distinguished two large islands.

Place names featuring *ner- or *nar- are wide-ranging over the vast Proto-Baltic homeland, occupying western Russia before the Slavs.

From these few references, which are the only surviving evidence apart from glottochronology[62] and place name analysis, it would seem that the Balts of Pytheas' time were well past the Common Balto-Slavic stage, and likely spoke a number of related dialects.

Nevertheless, Pytheas did obtain latitudes, which, according to Strabo, he expressed in proportions of the gnōmōn ("index"), or trigonometric tangents of angles of elevation to celestial bodies.

In whatever mathematical form Pytheas knew the location, he could only have determined when he was there by taking periodic readings of the elevation of the pole (eksarma tou polou in Strabo and others).

The first Ionian philosopher, Thales, was known for his ability to measure the distance of a ship at sea from a cliff by the very method Pytheas used to determine the latitude of Massalia, the trigonometric ratios.

The astronomic model on which ancient Greek navigation was based, which is still in place today, was already extant in the time of Pytheas, the concept of the degrees only being missing.

[35] At that point, on the day of the Summer Solstice, the vertical rod of the gnōmōn casts a shadow extending in theory to the horizon over 360° as the Sun does not set.

The words are too ambiguous to make an exact determination of Pytheas' meaning, whether diurnal or spring and neap tides are meant, or whether full and new moons or the half-cycles in which they occur.

A gravitational theory (objects fall to the center) existed at the time but Pytheas appears to have meant that the phases themselves were the causes (αἰτίαι aitiai).

The only ancient authors we know by name who certainly saw Pytheas' original text were Dicaearchus, Timaeus, Eratosthenes, Crates of Mallus, Hipparchus, Polybius, Artemidorus and Posidonius.

Strabo, citing Polybius, accused Pytheas of promulgating a fictitious journey he could never have funded, as he was a private individual (idiōtēs) and a poor man (penēs).

The Stone Stories trilogy by Mandy Haggith (The Walrus Mutterer, 2018; The Amber Seeker, 2019; The Lyre Dancers, 2020) revolve around Pytheas of Massalia's journeys.