[2] In 1545, he accompanied the French envoy Louis Adhémar de Monteil, Count of Grignan, to the Diet of Worms as a junior secretary.

It is not known who his protector was on the trip,[7] which lasted for three to four years,[8] but one of his biographers, Maurice Sarazin, has suggested it may have been Cardinal Tournon, a celebrated diplomat and friend of the arts.

[8] In his 1586 book, Traicté des chiffres ou secretes manières d'escrire, he wrote: in Rome, I did all that was possible — talking to learned men versed in Roman antiquity, visiting and revisiting the marble reliefs, bronzes, medals and ancient cameos from which one might draw knowledge and instruction — but I couldn't restore anything.

[8] In December of that year she sent a letter to Tournon, requesting that Vigenère respond to an overture made by the secretary of the elderly king of Poland, Sigismond Auguste Jagellon, who had no children.

She specified Vigenère should interview the Polish diplomat verbally, verifying the proposal's authenticity, then facilitate the idea, all without revealing he had been authorized to do so by her.

[12] Nine years later, Vigenère wrote in detail about this incident in his book La description du Royaume de Poloigne, without naming himself or revealing that he could have held secrets.