If your yardstick is total combat deaths I would nominate Verdun. 20th Century war bloodiest war, and I'm sure since there was a fortress there to begin with there has been other fighting there throughout history.
Also thinking Verdun here, Alsace-Lorraine is a very fought over territory. Franco-Prussian war of 1870-71, 30 years war, a lot of late medieval warfare and every time the French got into fights with the Habsburgs, a lot of blood were spilled here.