The country was historically about evenly balanced between Catholic and Protestant, with a complex patchwork of majorities over most of the country. Geneva converted to Protestantism in 1536, just before John Calvin arrived there. One canton, Appenzell, was officially divided into Catholic and Protestant sections in 1597. The larger cities and their cantons (Bern, Geneva, Lausanne, Zürich and Basel) used to be predominantly Protestant. Central Switzerland, the Valais, the Ticino, Appenzell Innerrhodes, the Jura, and Fribourg are traditionally Catholic. The Swiss Constitution of 1848, under the recent impression of the clashes of Catholic vs. Protestant cantons that culminated in the Sonderbundskrieg, consciously defines a consociational state, allowing the peaceful co-existence of Catholics and Protestants. A 1980 initiative calling for the complete separation of church and state was rejected by 78.9% of the voters. Some traditionally Protestant cantons and cities nowadays have a slight Catholic majority, not because they were growing in members, quite the contrary, but only because since about 1970 a steadily growing minority became not affiliated with any church or other religious body (21.4% in Switzerland, 2012) especially in traditionally Protestant regions, such as Basel-City (42%), canton of Neuchâtel (38%), canton of Geneva (35%), canton of Vaud (26%), or Zürich city (city: >25%; canton: 23%).

When did Geneva convert to Protestantism?