When Was Pierre de Fermat Born?

Most biographies of Fermat still give 1601 as his birth year. However, Klaus Barner, Professor Emeritus of the University of Kassel, Germany, has discovered that this is incorrect (Barner 2001). Investigating in French archives, he found the following facts: In the baptismal register of the city of Beaumont, he read that Piere (with one “r”), son of Dominique Fermat, was baptized August 20, 1601. Other documents show that the name of Piere's mother was Françoise Cazenove. It seems that she, her son, and a daughter died after 1603. Sometime between 1603 and 1607, Dominique Fermat married a second time. His new wife, Claire de Long, bore him five children, among them a son named Pierre again, like his deceased half-brother. Unfortunately the baptismal registers from 1607 to 1611 are completely missing. But the mathematician's eldest son, Samuel, had written in the last line of the Latin epitaph of his father at the family grave in Toulouse:

"OB.[iit] XII. IAN[uarii] .M.DC.LXV. AET[ate] .AN.[norum] .LVII."

That is, Pierre de Fermat died on January 12, 1665, at the age of 57 years. This means he was born between January 13, 1607, and January 12, 1608, and most probably in 1607. Additional research led Barner to conclude that Fermat was born between October 31 and December 6, 1607 (Barner 2007). In 1631 Fermat was conferred the right to add the title of nobility "de" to his name.

Above: On the gravestone or memorial plaque for Petri de Fermat, which Barner reported is kept "in the storeroom of the Musée des Augustins in Toulouse" (2010), Fermat's son Samuel ended his epitaph with the inscription:

"OB.[iit] XII. IAN[uarii] .M.DC.LXV. AET[ate] .AN.[norum] .LVII."

(Photograph used by kind permission of Musée des Augustins, Toulouse, France. You may use it in your classroom; for all other purposes, please obtain permission from Musée des Augustins.)

References

Barner, Klaus (2001). “How old did Fermat become?,” NTM: International Journal for History and Ethics of Natural Sciences, Technology and Medicine (New series) 8(4), 209-228.

Barner, Klaus (2007). “Neues zu Fermats Geburtsdatum,” Mitteilungen der Deutschen Mathematiker-Vereinigung 15, 12-14.

Barner, Klaus (2010), personal communication (email) to Janet Beery, Editor, MAA Convergence, 19 June 2010.

Editor's Notes

This article was originally published as an appendix to Friedrich Katscher's article, "Extracting Square Roots Made Easy: A Little Known Medieval Method," which appeared in MAA Convergence in November of 2010.

Klaus Barner also published a biography of Pierre de Fermat titled "Pierre de Fermat (1601?-1665): His life besides mathematics" in the Newsletter of the European Mathematical Society (EMS), No. 42, December 2001, pages 12-16. The link is to a pdf of the entire issue of the December 2001 EMS Newsletter.