The ancient breed of wild horses of northern Middle-earth. Legends of Men said that their ancestors had been brought to Arda by Oromë.

One of the Mearas was captured by Léod of the Éothéod when it was just a foal. It grew up to be a great white horse, but when Léod tried to ride it, it threw him and he died. The horse then ran away. Léod's sixteen-year old son Eorl found the horse, and demanded that it give up its freedom in exchange for the life of his father. The horse agreed, and Eorl named him Felaróf.

Felaróf was the sire of the breed of horses that became known as the Mearas. These noble horses lived as long as men, and had amazing strength and intelligence. It was said that Felaróf could even understand the speech of men.

The Mearas would only allow the Lord of the Mark or his sons to ride them, otherwise they lived wild. The only exception to this was Gandalf, who tamed the greatest Mearas of recent years, Shadowfax and rode him throughout the War of the Ring.

The word 'Mearas' came from an Anglo-Saxon word meaning simply 'horses'. Its singular form would be 'mearh', but no character in Tolkien's world ever used that word.