Martin Luther, a professor of theology at Wittenberg University in Saxony, writes on October 31, 1517,  to his bishop, Albrecht von Brandenburg, protesting the sale of indulgences.

He encloses in his letter a copy of his "Disputation of Martin Luther on the Power and Efficacy of Indulgences", which will come to be known as the Ninety-five Theses.

Luther's primary concern is the sale of indulgences—papal grants of reduced punishment in the afterlife, including releases from purgatory.

First written in Latin, the theses are soon translated into German and widely distributed.

Summoned by church authorities to explain his writings, Luther becomes embroiled in further controversy and in 1520 writes his three most famous tracts, in which he attacks the papacy and exposes church corruption, acknowledges the validity of only two of the seven sacraments, and argues for the supremacy of faith over good works.

In 1521 Luther is summoned to appear before Emperor Charles V at the Diet of Worms.

Refusing to recant his writings, he is banned under the Edict of Worms.

Secreted away by the ruler of Saxony, Frederick the Wise, Luther retreats to the castle of Wartburg, where he works on a translation of the New Testament and writes numerous religious tracts.