What we know about the Veil
The Veil is not a physical barrier, a “curtain”, or an idea/metaphor like described by the Chantry: it is a magical vibration which repels the Fade. The source of this vibration is unknown.
However, most people consider it to be a barrier and the terms associated with it are usually ones used with fabrics: the Veil can be “torn” and the sound it makes when it “tears” is like “ripping cloth”.
Solas created it, presumably at Skyhold. The human scholar who tried to repeat the experiments used metal rods which drawn in thunders and lightning, incinerating himself. It’s safe to assume that the creation of the Veil was complex and dangerous. Would the process of its removal be equally dangerous?
The Veil severed the elven people from the Fade, thus making them lose their immortality and powerful magic and destroying Elvhenan.
There are no accounts or descriptions of a time when the Veil didn’t exist in human history. Humans were able to reach the continent (in -3100 Ancient) only after the creation of the Veil.
This might be because the Veil offers protection to humans against what seemed to be the world of the ancient elves: in places where the Veil is thin (and so the Fade close), elves feel quick and strong, while humans slow and heavy, struck by terrible headaches caused by the “too many vivid colors”. For this reason, the Veil might be the only thing allowing the humans to live in Thedas.
Dwarves were able to live in the Veil-less world, maybe thanks to their bond to the Titans. It is not known what would happen to them now, should Solas succeed in tearing down the Veil. We also don’t know how the Qunari would react to such a drastic change: would they be affected like humans? Or would they survive easily thanks to their special and mysterious blood?
The Veil tends to be weaker and frail in zones where much death is or was present. The spirits “press” against it, trying to reach the waking world because “attracted by death”.
It’s also thin during the night, when most people are sleeping and, consequently, dreaming.
Blood magic can “tear” the Veil, allowing demons and spirits to pass through, but the use of it makes dreaming - and thus reaching the Fade even if only while sleeping - extremely difficult.
The Veil can be “ripped” beyond repair if the deaths and use of blood magic have been too much, like in the case of the Brecilian Forest.
It’s almost impossible to seal the tears and strenghten the Veil with normal methods and ordinary magic: mysterious elven artifacts are apparently able to do so and the Anchor, bestowed by the Orb of Fen’Harel, is famously the only way to close the Rifts definitively.
Some plants (like felandaris) and giant spiders grow only where the Veil is thin. Also, other plants and animals can be Fade-touched in such places, that is gain magical properties due to the close presence of the Fade.
Recently, saarebas have been able to open Rifts thanks to lyrium, which granted them enhanced powers and the ability to - relatively - affect the Veil.
The Veil is an artificial construct and millennia of wars, battles, magical experiments and so on have weakened it tremendously: it’s been stated multiple times how frail it has become.
For this reason, it is going to collapse soon, either because Solas will succeed in his plan or simply because it cannot last anymore, especially after the “trauma” it endured with the Breach.
