Execution of Jan Hus
Also called: Hussite Wars, Burning of Jan Hus
On 6 July 1415 the Bohemian theologian Jan Hus, a critic of the Church, was condemned as a heretic by the Council of Constance and burned, leading to the Hussite Wars.

Václav Brožík · Public domain · Source
Hus, a former rector of the University of Prague, was influenced by the Englishman Wycliffe; he attacked the wealth of the Church and the sale of indulgences, held Scripture to be the sole standard of faith and preached in Czech. He came to the Council of Constance under a safe-conduct from Sigismund, the future emperor, but was arrested and, refusing to recant, was burned on 6 July 1415.
Outraged Bohemians formed the Hussite movement from 1419 and repeatedly defeated the crusades sent by emperor and pope (the Hussite Wars, to 1434). Wycliffe and Hus are counted as forerunners of Luther’s Reformation a century later.