Burned at the stake
Being burned at the stake was a common punishment for heretics.
Burning was a way for the Church to execute people, as clerics were forbidden to draw blood by the Council of Nicea. Burning at the stake was a loophole of sorts, since the common medieval belief was that burning did not "draw blood" as the blood supposedly boiled away in the fire. The original intent of the ban on drawing blood was to make a the Church non-violent organization; this loophole instead gave the clergy free use of a horrible method of execution.