What is "simultaneum"

n. 1 A simultaneous occurrence of unrelated events. 2 (context Christianity English) The shared use of a church for both Protestant and Catholic services.

A shared church, or Simultankirche, simultaneum or, more fully, simultaneum mixtum, a term first coined in 16th-century Germany, is a church in which public worship is conducted by adherents of two or more religious groups. Such churches became common in the German-speaking lands of Europe in the wake of the Protestant Reformation. The different Christian denominations (such as Roman Catholic, Lutheran, Reformed, or United, etc.), share the same church building, although they worship at different times and with different clergy. It is thus a form of religious toleration.

Simultaneum as a policy was particularly attractive to rulers who ruled over populations which contained considerable numbers of both Catholics and Protestants. It was often the opposite of cuius regio, eius religio and used in situations where a ruler was of a different religion than the majority of the people, and not strong enough to impose his religion on the population.

During the Nine Years' War (1688–1697), Louis XIV of France occupied the Electorate of the Palatinate, a Protestant region situated mainly in the western part of what is today Germany, where he introduced the simultaneum. At the end of the war the region returned to Protestant control, but a last-minute addition to the Treaty of Ryswick provided for a continuation of the simultaneum. Although intended to apply only to the Palatinate, the simultaneum was subsequently also applied in portions of Protestant Alsace (a region ruled by France, but where the Edict of Fontainebleau was not enforced).