A negative aspect of the prosperous 14th century was the growing power of Church. An institution protected by Charles IV and other deeply religious kings started to affect lives of ordinary people. Apart from hedonist behavior of rich priests, what mattered the most was the sale of “indulgence” – a fee that could buy forgiveness for sins. Many scholars and philosophers were protesting against this insult to Christian morality, among them Jan Hus, who was scrutinized for his radical opinions and burnt as a heretic at a church-held council in Switzerland. This resulted in an open war conflict between the Hussites and Sigmund, the Czech King, son of Charles IV.
The Hussite Movement was a significant part of Czech History, many of the key battles took place in Prague itself. The movement later divided into a radical and a restrained wing. The restrained Hussites formed a coalition with the Catholics and together crushed the radicals. Although the king managed to suppress the revolution, the majority of Czechs converted to various forms of Protestantism and left the Catholic Church.