Thalos was the second of the six rivers that rushed down from the Blue Mountains through Ossiriand to meet the great River Gelion, between the rivers Ascar and the Legolin. It was in the high valley of its upper course that Bëor and his followers, the first Men to cross into Beleriand, made their camp, and where they were discovered by Elf King Finrod Felagund.
- J.R.R. Tolkien, Christopher Tolkien (ed.), The Silmarillion, "Map of Beleriand and the Lands to the North"
- J.R.R. Tolkien, Christopher Tolkien (ed.), The Silmarillion, "Quenta Silmarillion: Of the Coming of Men into the West"
- J.R.R. Tolkien, Christopher Tolkien (ed.), The Lost Road and Other Writings, Part Three: "The Etymologies", entry "STAL"
|Seven Rivers of Ossiriand|
|Gelion · Ascar · Thalos · Legolin · Brilthor · Duilwen · Adurant|