The French author Alphonse Rebière, in his work Mathématiques et mathématiciens of 1889, tells that Tsar Ivan IV of Russia, nicknamed "the Terrible", once posed a problem to a geometer of his court. It was a matter of determining how many bricks would be required to construct a regular building, the dimensions of which were indicated. The answer was quick and the construction made later demonstrated the accuracy of the calculations.
Ivan, impressed by this fact, had the mathematician burned, persuaded that by doing so he would rid the Russian people of a dangerous sorcerer.
Ivan IV or Ivan IV, Tsar of Russia
Another curious fact was that the famous François Viète, founder of Modern Algebra and gifted mathematician, was also included among the wizards and sorcerers of his time.
Historians report that during the civil wars in France, King Henry IV intercepted a secret order from Spain, which was passed to Viète. The mathematician then deciphered a secret code that the Spaniards created for correspondence, which featured some 600 different symbols, periodically exchanged by a rule that only the closest subjects of the Spanish king Felipe II knew.
When Philip II learned that the enemies had discovered the secret of the code, which had hitherto been undecipherable, it led Pope Gregory XIII to denounce that the French resorted to the evil spells of witchcraft, a denunciation that the pope did not pay the slightest attention.
Reference: Adapted from "Fun and Curious Math". TAHAN, Malba