Many people truly believe that thousands of innocent women were burned in Europe in the Middle Ages. But in fact, up to the 15th century, the church denied the fact that witches existed. The mass witch hunt started in the 16th and 17th centuries. The reason for this was the plague pandemic.
The diseases spread so quickly that 24% of the European population died in just several years. There was no remedy for it and people were in such a panic, they thought that it was caused by witchcraft. So by the 16th century, both the church and regular people were scared of magic and executed everything who had any connection to it. But witches were burned only to demonstrate this to people. Most of the time, they were hanged — this was the most popular way of execution.