His attitude exposed him to the animosity of the League party and of the Holy See, and to their persecution when the first edition of his history appeared. This history was his life's work. In a letter of 31 March 1611, addressed to the president Pierre Jeannin, he described his labours. His materials were drawn from his rich library, which he established in the Rue des Poitevins in the year 1587, with the two brothers, Pierre and Jacques Dupuy, as librarians. His object was to produce a scientific and unbiased work, and for this reason he wrote it in Latin, giving it as title "Historia sui temporis". The first 18 books, embracing the period from 1545–1560, appeared in 1604 (1 vol. folio), and the work was at once attacked by those whom the author himself calls "les envieux et les factieux".