They called him antiquity's biggest liar. They used his numbers anyway

When

c. 325 BC

Distance on the map

1,850 kmat least, along the drawn route

By way of

Massalia (Marseille), the Pillars of Heracles, Burdigala (Bordeaux)

Dashed: the two hypotheses for leaving the Mediterranean. No source says which he chose.

Massalia, the Greek colony where Marseille now stands, was around 325 BC a wealthy trading city that still depended on Carthage's goodwill for access to the ocean beyond the Pillars of Heracles. The Carthaginian fleet controlled the strait; a Greek merchant who wanted to reach the tin of the north needed either Carthage's permission or a way around it.

Pytheas was, in Polybius's words, “a private individual, and a poor one at that,” not an aristocrat with a fleet of his own. How he funded the expedition is unknown; Cunliffe has suggested Massalia itself paid for it, keen to open a direct route to tin that otherwise passed through Carthaginian hands.

Before he left, or on his return, he measured at Massalia the ratio of a gnomon to its shadow at noon on the summer solstice: 120 to 41 and four fifths. It is his one astronomical measurement that can still be checked today with precision, because the geometry of the solstice sun has not changed. The calculation gives Massalia a latitude of about 43°, within half a degree of the real figure. On that number, two centuries later, Hipparchus would build a calculation of his own, the only case in antiquity of someone actually checking one of Pytheas's results with their own instruments.

What is not known is how he left for the Atlantic. One route takes him by sea, along the Iberian coast, through the Pillars of Heracles, under the eyes of the Carthaginian fleet. The other, supported by a much later text, Avienus's Ora Maritima, which appears to preserve an old Massaliote sailing guide, takes him overland and by river: up the Rhône, then a portage to the Garonne, down to Burdigala, today Bordeaux, avoiding the strait entirely. No fragment of On the Ocean says which is true.

When

c. 325 BC

Distance on the map

2,060 kmat least, along the drawn route, of which 1,670 km on an assumed route

By way of

Uxisame (the Ostimii)

Dashed: the approach to the Bay of Biscay, on either route. Solid: the coastal run to the Ostimii, where the order is confirmed independently.

Whichever way he left the Mediterranean, both routes lead into the Bay of Biscay, and from there north-west along the Atlantic coast of Gaul. The first place the sources tie firmly to his account belongs to a tribe Strabo calls the Ostimii, correcting the form Pytheas himself apparently used, for the people known today as the Osismii, at the very tip of Brittany.

Strabo writes that their promontory “does not project so far into the ocean as he and those who have trusted him say.” The sentence does two things at once: it says Pytheas exaggerated a distance, and it admits that, three centuries after him, readers still existed who were willing to believe it. The island of Uxisame, today Ouessant (Ushant), which Pytheas places three days' sail out, is for Strabo simply “an invention.”

He is wrong about that: Ushant exists exactly where the ancient sources that cite Pytheas place it, even if the sea distance he gives looks inflated. It is the first instance of a pattern that repeats at every leg of the voyage: an exaggerated or unverifiable figure, sitting beside a real, correctly identified place.

When

c. 325 BC

Distance on the map

180 kmat least, along the drawn route

By way of

Belerion (Cornwall)

Solid: the short coastal run from the Ostimii to Belerion, the western tip of Cornwall.

Belerion, the ancient name for the western tip of Cornwall, was the centre of Europe's prehistoric tin trade long before Pytheas. Not one sentence from On the Ocean about Belerion survives under his name. What survives is a technical description, in Diodorus Siculus, three centuries later, which never mentions him at all.

Diodorus writes that the people of Belerion, “by reason of their converse with merchants, are more civilized and courteous to strangers than the rest are,” that they dig the tin “with a great deal of care and labour” out of rocky ground, melt it, refine it, and beat it “into four-square pieces, like to a dye,” which they carry to a nearby island, Ictis, reached over dry ground at low tide. From there, merchants bought it and carried it overland across Gaul, to the mouths of the Rhône, toward Massalia.

Historians are nearly unanimous: technical detail this precise, the size of the ingots, the mechanics of the tide, could hardly come from anywhere but a direct visit, and the only Greek known to have reached the place at that date was Pytheas. The chain of transmission most likely runs through Timaeus of Tauromenium, who read Pytheas, and whom Diodorus, in turn, read. Pytheas's name was lost somewhere along the way; his knowledge of Belerion was not.

When

c. 325 BC

Distance on the map

1,460 kmat least, along the drawn route, of which 950 km on an assumed route

By way of

Cantium (Kent), Orcas (Orkney)

Solid: the south coast, as far as Cantium, the one stretch of the circuit confirmed by more than one source. Dashed: the rest of the circuit, including the direction it went.

Pytheas claimed, Strabo says through Polybius, to have “travelled over the whole of Britain that was accessible,” and reported that the island's coastline measured more than forty thousand stades, somewhere between 6,000 and 7,400 kilometres depending on which ancient stade is used. Britain's coastline does not, in fact, have a fixed length: the finer the instrument used to measure it, the more inlets it finds, and the larger the number grows, a phenomenon known today as the coastline paradox. Pytheas's figure can be neither confirmed nor refuted directly for that reason; it remains, at least, the right order of magnitude, not inflated by a wild factor the way other ancient travellers' claims sometimes were.

The one stretch of the circuit more than one source confirms is the south coast, as far as Cantium, today Kent, which Strabo gives as “several days' sail from Celtica.” From there onward, the modern map of the voyage is a guess: it is not known whether Pytheas circled the island eastward or sailed directly north along the west coast.

What is known is that he eventually reached the northern tip of Britain, at a place later sources call Orcas, today's Orkney Islands. From there, he says, began the last leg of the voyage: six days' sail north, to Thule.

When

c. 325 BC

Distance on the map

1,990 kmat least, along the drawn route

By way of

Thule? (Shetland), Thule? (Iceland), Thule? (the Norwegian coast)

Dashed on all three branches: Shetland, Iceland and the Norwegian coast all remain possible candidates for Thule.

Of everything Pytheas wrote, one sentence survives in his own words, not someone else's paraphrase. Geminus, an astronomer of the first century BC, preserves it, citing it as a technical source for the phenomenon of short nights in the north: “The barbarians showed us the place where the sun goes to rest. For in those parts the nights were very short, in some places two hours, in others three, so that the sun rose again a short time after it had set.”

A night of two or three hours corresponds, by the geometry of the sun's position at the summer solstice, to a latitude of roughly 64–65° north: the south coast of Iceland, the Norwegian coast around Trondheim, or, on a generous reading of the “six days,” even Shetland understood as the edge, rather than the neighbourhood, of Britain. All three remain serious candidates today; none has settled the question.

Strabo believes none of it. “The man who tells about Thule, Pytheas,” he writes, “has been found, upon scrutiny, to be an arch-falsifier.” A few pages later, about the same reports, he adds: “if judged by the science of the celestial phenomena and by mathematical theory, he might possibly seem to have made adequate use of the facts as regards the people who live close to the frozen zone.” It is the closest Strabo comes, anywhere in the text, to admitting that Pytheas's numbers might stand even if the man, in his view, does not.

Of life there, Pytheas also said, again through Strabo, that the people live on millet, herbs, fruit and roots, and that the grain, “since they have no pure sunshine,” is threshed indoors, in large storehouses, under a roof.

When

c. 325 BC

Distance on the map

1,690 kmat least, along the drawn route

By way of

Skagen (the Danish strait), Sambia? (the amber coast)

Dashed along the whole route: the passage through the North Sea and the Danish strait, and the identification of the island of Abalus, both remain guesses.

Pliny the Elder, three and a half centuries later, quotes Pytheas with a precision he grants no other fragment: “Pytheas speaks of an estuary of the Ocean named Metuonis, seven hundred and fifty miles long, the shores of which are inhabited by a German tribe, the Guiones. From there it is a day's sail to the island of Abalus, where, he says, amber is carried in spring by currents, being an excretion of a congealed brine.” The inhabitants burn it as fuel, in place of wood, and sell it to their neighbours, the Teutones.

Timaeus, Pytheas's contemporary as quoted later by Pliny, largely confirms the story, but calls the island Basilia, not Abalus. That two independent authors, a few decades apart, give a similar account of an amber island in the Baltic suggests a real common source rather than literary invention, even though the exact location of the island, the Sambian peninsula being the best-supported modern candidate, remains disputed.

Whether Pytheas saw the amber coast himself, sailing around Scotland and down through the North Sea to the Danish strait, or gathered the information from merchants met further north, is a question the sources never settle. The distance and direction he gives are plausible; that alone does not prove he was there.

When

c. 325 BC

Distance on the map

5,270 kmat least, along the drawn route

By way of

Massalia (Marseille)

Dashed along the whole route: no source says how he got back to Massalia.

No line, in any source, says how Pytheas returned to Massalia, or how long the whole voyage took. The map draws, dashed, the shortest way back, through the same assumed waters as the outward leg; it is a convenience of symmetry, not a claim.

On his return, he wrote a book, On the Ocean. The title is the one thing certain about it: no manuscript survives, no papyrus fragment, no medieval copy, of the kind that preserved, at least in part, the texts of Strabo or Pliny. Everything that can be read of Pytheas's book passes, without exception, through someone else's pages, people who each had their own reasons to quote him, either to argue against him or to support their own calculations.

Eratosthenes, the geographer who measured the circumference of the earth, used his data on Britain without ever questioning his honesty. Hipparchus took his gnomon ratio from Massalia and used it to fix, he believed, Byzantium's latitude on the same parallel. Here he was wrong, but the error is Hipparchus's, not Pytheas's: Byzantium's real latitude lies more than two degrees further south than Massalia's, an error of more than 200 kilometres that Hipparchus introduced, two centuries later, by reusing the figure of a man other writers called a liar.