Balefire

Balefire is the green flame burned within Gravehollow to deter Rogue Undead from entering settlements. It is burned in large braziers usually within the center of towns or villages.
Undead avoid the presence of Balefire and will run from it if it gets to close to them. If an undead is set aflame with balefire it will be permanently destroyed.
Sentient Undead such as Liches, Death Knights and Wights note that they feel discomfort near Balefire but feel no compulsion to run from it.
The Origins of Balefire are unknown but it is known to predate the Old World as it appears in the records of the Giants.
Lanterns that burn Balefire can be purchased in most Alliance cities. these lanterns need no fuel to continue burning.