The Blue Mountains

Originally Eriador was largely forested, but in the Second Age Dúnedain felled most of the forests to build ships. In the late Second Age and early Third Age, much of Eriador was encompassed by the kingdom of Arnor, which later split into the rival kingdoms of Rhudaur, Arthedain and Cardolan. The Shire occupied part of the former kingdom of Arthedain, while Bree and its neighbouring villages lie on the border with the former Cardolan. The Barrow-wights dwelt within ancient burial mounds which had been constructed in the First Age by the Edain as they journeyed to Beleriand.[3] Other important places in Eriador were Rivendell, the Grey Havens and the abandoned kingdoms of Eregion andAngmar.

Population and settlements
For much of Middle-earth's history, Eriador was sparsely populated, and indeed this is the meaning of its name: the Lone-lands. By the time of the War of the Ring, the main settlements were the Shire, Bree-land, Rivendell and the Grey Havens. Communities of Dwarves still mined the Ered Lindon, and a small population of native Men maintained ahunter-gatherer culture in the remaining woods of Minhiriath.[4] Eriador was protected by the Rangers of the North, who were the surviving Men of the lost kingdom of Arnor.

Geography
The boundaries of Eriador were: Eriador extended for some 600 miles north-south and 700 miles west-east. It was traversed by two main routes:- Important rivers were the Lune (Elvish Lhûn), the Brandywine (Elvish Baranduin) and the Greyflood (Elvish Gwathló).
 * To the east: the Misty Mountains. On the further (i.e. eastern) side of these mountains lay the region of Rhovanion (Wilderland).
 * To the north: the Northern Waste (Forodwaith) and — after the War of Wrath and ensuing floods which ended the First Age — the Ice-bay of Forochel.
 * To the west: the mountains of Ered Lindon (also known as Ered Luin or Blue Mountains). On the far (i.e. western) side of these mountains lay the region of Lindon, which was virtually the only part of Beleriand that had survived the First Age. The Grey Havens were located in a gap in the Ered Luin, and it's not clear whether these havens (and the adjacent lands west of the Tower Hills) were part of Lindor or Eriador.
 * To the south: the rivers Glanduin and Greyflood (forming the border with the land of Enedwaith) and the shores of Belegaer west of Lond Daer.
 * the East-West Road running from the Misty Mountains' High Pass (near Rivendell) to the Grey Havens
 * the Greenway (formerly the North-South Road connecting the kingdoms of Arnor and Gondor).

Depictions in adaptations
Eriador was the initial setting of the Lord of the Rings Online video game. Notably, both Gandalf, who narrates, and characters in-game refer to various dangers as "The Doom of Eriador" or "A Threat to all of Eriador" instead of Middle-earth as a whole. The game was later expanded to include other regions of Middle-earth, such as Moria, Lothlorien and Mirkwood.