Typically, when a person was burned at the stake, they were first mercifully dispatched with the garotte. Either the executioner would use a rope, or he would use an instrument like the one pictured here.
At first, the garotte was simply hanging by another name. However, during Medieval times, "executioners began to refine the use of rope until it became as feared and as vile as any punishment of that dark era. European executioners first used the garotte to end the suffering of men broken on the wheel, but by the turn of the 18th century the seed of an idea involving slow strangulation was planted in the minds of Europe's law-makers."
At first, garottes were nothing more than an upright post with a hole bored through. The victim would stand or sit on a seat in front of the post, and a rope was looped around his or her neck. The ends of the cors were fed through the hole in the post. The executioner would pull on both ends of the cord, slowly strangling the victim.
The modified design we see on top drove a spike into the back of the victim's neck, parting the vertebrae as it strangled. Sometimes a knife was used instead of the spike.