The ''Declaratio Ferdinandei'' () was a clause in the Peace of Augsburg, signed in 1555 to end conflicts between

Catholics The Catholic Church (), also known as the Roman Catholic Church, is the largest Christian church, with 1.27 to 1.41 billion baptized Catholics worldwide as of 2025. It is among the world's oldest and largest international institut ...

and

Protestants Protestantism is a branch of Christianity that emphasizes Justification (theology), justification of sinners Sola fide, through faith alone, the teaching that Salvation in Christianity, salvation comes by unmerited Grace in Christianity, divin ...

within the

Holy Roman Empire The Holy Roman Empire, also known as the Holy Roman Empire of the German Nation after 1512, was a polity in Central and Western Europe, usually headed by the Holy Roman Emperor. It developed in the Early Middle Ages, and lasted for a millennium ...

. The Peace created the principle of '' Cuius regio, eius religio'' (Latin for "''whose realm, his religion''"), which meant that the religion of the ruler decided the religion of the inhabitants. The ''Declaratio Ferdinandei'' exempted knights and some of the cities under the jurisdiction of an ecclesiastical prince if they had practiced

Lutheranism Lutheranism is a major branch of Protestantism that emerged under the work of Martin Luther, the 16th-century German friar and Protestant Reformers, reformer whose efforts to reform the theology and practices of the Catholic Church launched ...

for some time (Lutheranism was the only branch of Protestantism recognized under the Peace). The provision was not publicized as part of the treaty, and was kept secret for almost two decades. After Catholic victories early in the

Thirty Years' War The Thirty Years' War, fought primarily in Central Europe between 1618 and 1648, was one of the most destructive conflicts in History of Europe, European history. An estimated 4.5 to 8 million soldiers and civilians died from battle, famine ...

, the ''Declaratio Ferdinandei'' was overturned in the Edict of Restitution of 1629, which was part of Ferdinand II's master plan to reconvert the Holy Roman Empire to Catholicism.Parker, pp. 87–88 The overturning of the ''Declaratio Ferdinandei'' and other religious persecution helped rekindle the Thirty Years' War, changing it from an internal conflict within the Holy Roman Empire into an international religious war.

References

Augsburg Augsburg ( , ; ; ) is a city in the Bavaria, Bavarian part of Swabia, Germany, around west of the Bavarian capital Munich. It is a College town, university town and the regional seat of the Swabia (administrative region), Swabia with a well ...

Latin words and phrases

Christianity in the Holy Roman Empire 1555 establishments in the Holy Roman Empire 1629 disestablishments in the Holy Roman Empire 1555 in Christianity 1555 treaties {{Treaty-stub

See also

References