Here and there upon heights and ridges they caught glimpses of ancient walls of stone, and the
ruins of towers: they had an ominous look. Frodo, who was not walking, had time to gaze ahead and to think. He recalled Bilbo's account of his journey and the threatening towers on the hills north of the Road, in the country near the Troll's wood where his first serious adventure had happened. Frodo guessed that they were now in the same region, and wondered if by chance they would pass near the spot. 'Who lives in this land?' he asked. 'And who built these towers? Is this troll-country?' 'No!' said Strider. 'Trolls do not build. No one lives in this land. Men once dwelt here, ages ago; but none remain now. They became an evil people, as legends tell, for they fell under the shadow of Angmar. But all were destroyed in the war that brought the North Kingdom to its end. But that is now so long ago that the hills have forgotten them, though a shadow still lies on the land.'
J.R.R Tolkien, The Lord Of The Rings, The Fellowship Of The Ring, Chapter 12 Pages 217-218