 He was finally forced to flee France during the Affair of the Placards in mid-October 1534.In that incident, unknown reformers had posted placards in various cities criticizing the Roman Catholic mass, to which adherents of the Roman Catholic church responded with violence against the would-be Reformers and their sympathizers.In January 1535, Calvin joined Cop in Basel, a city under the enduring influence of the late reformer Johannes Oecolampadius.