Four Thieves Oils

During the black death (the black plague) epidemic of the medieval period, this oil was used to prevent the catching of the plague. The Four Thieves Formula was also used as a vinegar. Similar herbal based vinegars have been used as medicine since the of Hippocrates. Many early herbals for this have been added into this oil or vinegar recipe.

The Museum of Paris in 1937 hung up a recipe of this vinegar. They said it to be the original recipe but research is shown to be different ingredients.

The ingredients:

Take three pints of strong white wine vinegar, add a handful of each of wormwood, meadowsweet, wild marjoram and sage, fifty cloves, two ounces of campanula roots, two ounces of angelic, rosemary and horehound and three large measures of camphor. Place the mixture in a container for fifteen days, strain and express then bottle. Use by rubbing it on the hands, ears and temples from time to time when approaching a plague victim.

This also another recipe:

Another recipe called for dried rosemary, dried sage flowers, dried lavender flowers, fresh rue, camphor dissolved in spirit, sliced garlic, bruised cloves, and distilled wine vinegar.

Mythology

During the black death four thieves use this oil/vinegar to rob the dead that died of the plague. They where caught and forced to give up the secret recipe. 

Another tale, the Four thieves was caught robbing the sick. Their punishment was to bury the plague victims. Through this punishment they developed this recipe to survive this ordeal. 

Theory

The four thieves vinegar/oil could be a corruption of Forthave's Vinegar. Forthave's Vinegar is a concoction sold and invented by Richard Forthave.