Marauders are typically found in out-of-the-way ruins, fort ruins and caves. As their name implies, they're doing probably the same thing the Hero is doing: Plundering the place for riches and treasure. They behave like bandits, but are generally better-equipped, perhaps as a result of selling their loot, or else simply finding good armor in the many abandoned forts, caves, and ruins they have already plundered.