When Turbine looked at designing the areas of Middle-earth, some regions, like The Shire, were blessed with several detailed maps which could serve as invaluable reference material. Other regions, however, were less well mapped, and some, like the Ered Luin and the surrounding lowlands, were hardly mapped at all.
The Ered Luin (Blue Mountains) are one of only a few surviving features of Beleriand, the far north-western area of Middle-earth which was destroyed at the end of the First Age. The mountains were homes to two important Dwarf settlements, Nogrod and Belegost. We are told in The Silmarillion that both were ruined in The War of Wrath, when Thangorodrim was broken and Beleriand was submerged. The Ered Luin themselves were thrust apart in their midst and the sea rushed in, creating the Gulf of Lhun and changing the course of the river.
The lands to the west of the mountains were in the First Age called Ossiriand, the land of seven rivers, and was also named Lindon by the Noldor. It was settled by Nandorin (Green) Elves and for a time housed both Beren and Luthien towards the end of their lives. East of the mountains the land rolled away into downs and thus to Eriador.
It is important to note that the Ered Luin and surrounding lands have been home to Dwarves as well as Nandorin, Sindarin and Noldorin Elves, but never to any significant groups of Men. In this Turbine have been consistent.
