The Tower Hills were a series of steep hills at the west end of Eriador.
They lay about 30 Númenórean miles east of Mithlond, the Grey Havens of Lindon, and about 50 miles west of the White Downs, of old the border of the Shire.
High upon the Tower Hills, or Emyn Beraid in Sindarin, stood three tall Elven towers, the highest of which was called Elostirion and held a Palantír.
The Tower Hills formed the ancient border between the Elven realm of Lindon and the Kingdom of Arnor, and the Great East Road which led all the way to Rivendell ran through them.
In the early Fourth Age, Elanor daughter of Samwise Gamgee and her husband Fastred moved to the Tower Hills, founding the town of Undertowers on the eastern slopes of the Hills, and becoming the Wardens of Westmarch, when the Tower Hills became the new western border of the Shire.