A theory about the raising of the veil and the loss of immortality for the elves, as I mentioned in the Solas discussion thread. This is based on data from the in-game codex and the dragon age wiki:
So what if the slaves of ancient arlathan willingly sacrificed their immortality to erect the veil? This for the promise of freedom. They used their combined will/faith to have death come to pass for the first time ever in order to raise the veil and be free. The skyhold codex 2nd entry leads me to believe this:
Spoiler
Skyhold has not just been claimed time and again, but sacked as well. We've managed to uncover some remnants, including a scratching under a pillar that mentions the name given by your witch. Old but still long after the place had been built over. But the author knew something of its first purpose, or at least, something of a legend.
Var'landivalis him sa'bellanaris san elgar
Melanada him sa'miras fena'taldin (word missing)
Nadasalin telrevas ne suli telsethenera
Tarasyl'an te'las vehn'ir abelath'vir (word missing)
Even with assistance from your elf, we managed only a partial translation. Elven is often a game of intents, not direct mapping of phonetic meaning. That means it's a mess.
Our belief transformed into everything. (assertation/problem? uncertain)
All time is transformed into the final/first death (uncertain),
inevitable/threatened victory and horrible/promised freedom in the untorn veils, (uncertain)
Where the sky is held up/back, where the people give/gain love that is an apology/promise from/to....(missing subject, uncertain)
Mostly complete, as fragments go. The rhythm is strange, not like others I've recorded. Perhaps less a poem than a statement? The elven language does tend to meander.
-- Notes from the archivist
It's not much of a jump to theorize that Fen'Harel helped them do this. Fen'Harel always demands a heavy price for his help does he not? And he's now known as a rebel/trickster. He tricked the gods to be trapped behind the veil and as such set their slaves free....at a cost.
Why give up their immortality?
They were desperate. They wanted to be free, I'm guessing at that point the rebellion wasn't doing so well: "inevitable/threatened victory and horrible/promised freedom in the untorn veils, (uncertain)" . It was either be dragged back into slavery/dying anyway or make a huge gamble. They gambled and now it turns out they lost as the elves are still not exactly free. Not sure if it killed the elves immediately in the ritual or just cut away the inherent magic that made them immortal, they could have lived human lifespans after this, making it not exactly suicide.
There is the Slow Arrow tale told by Felassan and the codex of Abelas in the temple of Mythal that could suggest that only the elders died/went into uthenera to conduct the ritual and the young ones were left behind without the wisdom of their elders to guide them. Resulting in the loss of much of their combined knowledge.
Spoiler
The god Fen'Harel was asked by a village to kill a great beast. He came to the beast at dawn, and saw its strength, and knew it would slay him if he fought it. So instead, he shot an arrow up into the sky. The villagers asked Fen'Harel how he would save them, and he said to them, 'When did I say that I would save you?' And he left, and the great beast came into the village that night and killed the warriors, and the women, and the elders. It came to the children and opened its great maw, but then the arrow that Fen'Harel had loosed fell from the sky into the great beast's mouth, and killed it. The children of the village wept for their parents and elders, but still they made an offering to Fen'Harel of thanks, for he had done what the villagers had asked. He had killed the beast, with his cunning, and a slow arrow that the beast never noticed.
--Felassan, to Briala
I don't think he did it out of malice. Raising the veil would require power, a lot of power. I imagine the kind of power only the sacrifice of the immortality of an entire people would give. He cares about the People, he wants them to be free. History shows that things didn't go well for the elves but that was never Fen'Harel's intent.
So what is Fen'Harel/Solas up to?
This is basically idle speculation: my guess after seeing the time warp in the mage playthrough and certain lines in Sera's song is that Solas will attempt to undo the past. Which might mean go back in time to stop the sacrifice of elven immortality to raise the veil. And Sera for one will be there to stop him (I tend to go with the theory someone made that Sera is Andruil without her knowing it based on the vallaslin and tarot cards, sorry I don't have the link).
Some lines that stand out for me in Sera's song:
Spoiler
Sera was never an agreeable girl -
Her tongue tells tales of rebellion.
But she was so fast,
And quick with her bow, No one quite knew where she came from.
Sera was never quite the quietest girl -
Her attacks are loud and they're joyful.
But she knew the ways of nobler men,
And she knew how to enrage them.
She would always like to say, "Why change the past,
When you can own this day?"
Today she will fight,
To keep her way.
She's a rogue and a thief,
And she'll tempt your fate.
Sera was never quite the wealthiest girl -
Some say she lives in a tavern.
But she was so sharp,
And quick with her bow - Arrows strike like a dragon.
Sera was never quite the gentlest girl -
Her eyes were sharp like a razor.
But she knew the ways of commoner men,
And she knew just how to use them.