After the third great battle between the elves and Morgoth (Dagor Aglareb), Beleriand settled into a watchful peace and the elves — both Sindar and Noldorin — established the boundaries of their kingdoms. This is all recorded in Of Beleriand and its Realms — the 14th chapter of the Silmarillion.
We wonder, though, who is telling the tale? From what era? Could it be a Sindar elf, a Noldor lord? Or even a hobbit, perhaps?
Descriptions of the slag and ash-heaps of Thangorodrim, for example, are remniscent of the fields outside Mordor’s gate. With smoke constantly issuing from its lofty peaks, Thangorodrim itself feels like a forerunner of Mt Doom. [More]