Pierre de Fermat was one of the most recognized mathematicians of his time, and perhaps in all of history. He was infamous for making claims of mathematical proofs in the margins of documents without actually giving the proof. Ever since, mathematicians have struggled to prove his theorems. His Last Theorem, which relates to number theory, wasn’t proven until 1994, some 358 years after Fermat made his claim, by the mathematician Andrew Wiles. One interesting tidbit about Fermat is that many sources and sites state he was of Basque origin. But was he really?

• Not much is known of Fermat’s youth. He was born in late 1607 in the French city of Beaumont-de-Lomagne to a family of leather merchants. His father, Dominique Fermat, was second consul of the town, and his mother was Claire de Long. (I’ve seen other sources say he was born in 1601 and his mother was Françoise Cazenove, but this seems to be a different Piere that was born to Dominique’s first wife Françoise, not the famous mathematician.)
• Many places say that Fermat had Basque ancestry, and a few claim he spoke Basque fluently. Unfortunately, I’m not able to find any original sources for these claims. It seems this claim started with an Encyclopedia Britannica article that stated that “He was of Basque origin…” Other online sources claim that “He was born into a Basque family of leather merchants” and that he “was an accomplished linguist fluent in… Basque.” However, when I dig deeper, I can’t find any real evidence for these claims.
• If you look at his ancestry, you don’t find any Basque names. Instead, in addition to Fermat (of course), there are names like de Long, L’Hospital, Bernuy, and Lagriffoul. Nothing obviously Basque that I can find.
• What is clear is that Fermat was born in Gascony, and that his family had been in Gascony for at least a few generations. The current province of Gascony lies just north of Iparralde. The Gascons are certainly historically related to the Basques, and indeed the word Gascon comes from the same root. But those connections are quite ancient. If the Gascons spoke a language related to Basque, it was eventually lost and replaced with modern Gascon, a Romance language. Interestingly, however, Gascon does seem to have a Basque substrate, or influence.
• Another piece of evidence that Fermat was Gascon and not Basque comes from René Descartes, another of the great French mathematicians and an intellectual rival. He is quoted as having said “Fermat is Gascon, not me.” At the time, calling someone a Gascon was to call them a braggart.
• So, it seems clear that, in the end, Fermat was not Basque, but rather Gascon. This is of course neither here nor there. It seems that the original British author, when putting together the entry for the Encyclopedia Britannica, simply confused Basque and Gascon, and that confusion has then been repeated and spread without any further investigation.

Primary sources: All sources are linked in the article, but I’d like to give particular thanks to Eneko Sagarbide who helped track down these sources and claims about Fermat’s true origins.