*Spoilers for Tresspasser*
I know this topic of the Deep Roads in Tresspasser been brought up before, but I found this (below) in the Deep Roads from the Eluvian in Tresspasser. Could this be where Mythal slayed the titan?
As you enter, Cole says that the place has "forgotten how to be". We also know, that thaigs should be naturally lit up, yet this one isn't.
Also, there is elven architecture throughout the thaig, including statues to Fen'Harel, so this could be the Lyrium mine they made once Mythal killed the Titan.
Could it be because of the death of the Titan?
Also, this probably explains why the Eluvian would lead to The Deep Roads in the first place.
Lastly, why would the Ancient Elves need Lyrium to begin with? There was no veil, and their magic didn't require Lyrium to strengthen their connection to The Fade, as there was no such thing as The Fade at the time. Was it the reason the Evanuris were so powerful to be "worshipped"?
Just some food for thought, dareth shiral 💚