In this case, I'd say it's a combination of definition 1 and 3. The "story" of the Battle of Verdun is definitely quite famous and is part of the larger narrat

In this case, I'd say it's a combination of definition 1 and 3. The "story" of the Battle of Verdun is definitely quite famous and is part of the larger narrative around WWI. While it's obviously not a person, it has some of the legendary aspects that fit into definition 3. In general, the popular definition of "legend" includes practically any aspect of popular history.