 The spread of Protestantism and the application of its fundamental principle of private judgment produced far-reaching differences in belief.To heal these and so bring about unity, a conference was held at Weimar in 1560, between the Lutherans Viktor Striegel (1524–69) and Flacius, on free will.The Poissy conference was arranged by Catherine de' Medici, the Florentine Catholic queen-mother and regent during the minority of her son, Charles IX of France, with the support of the Chancellor Michel de l'Hôpital and the lieutenant-general of the kingdom, Anthony of Navarre.