The word 'Mark' comes from Old English mearc, which would presumably have been the form familiar to the Rohirrim themselves. It signifies a borderland, especially a land that protected the heartland of another realm (as the Mark of Rohan did Gondor). The name is cognate with 'Mercia', the name of an old Anglo-Saxon kingdom in central England, and also appears, for example, in 'Denmark', the 'borderland of the Danes'.