in 1630 when the Great Plague swept through Toulouse, France. Four thieves ransacked the city without contracting the disease; when finally caught, a judge decided to commute their death sentences, if they revealed the secret ingredients to the mysterious decoction that gave them immunity from the disease. The formula now known as the“The 4 Thieves Vinegar” was a combination of thyme, lavender, rosemary and sage steeped in vinegar. One hundred years later the disease struck again in Marseilles. Herbalists then added garlic as the fifth ingredient. In the 19th century a French distiller of vinegar patented the formula and marketed this elixir to nuns, priests and doctors. “Drink some on an empty stomach in the morning. In London around the same time, during the Black Death, it was suggested that a bunch of lavender fastened to each wrist would protect the wearer against the deadly disease.

This story could have some validity as the plague was transmitted by fleas, which lavender is known to repel.

http://www.complete-herbal.com/details/lavender.html