This could be considered a sort of prelude to that one fanfiction idea I had, about the time when Discord ruled Equestria. This would be the history of the alicorns.
They weren't always immortal. Once, they were just a race of powerful unicorns. But then a great and terrible magic was discovered - the magic that could change a unicorn, and put them beyond the touch of time...Truly an amazing feat, the greatest magic ever discovered. But when the rich and powerful could live forever, and the rest were doomed to die...that magic became the catalyst of a great war. Tyrants and armies without end waged a war for the secret of everlasting life. And in the end, all perished.
Except for two young mares, left in the ashes of a once great kingdom.
Came up with this when I was thinking about the season finale, and how a particular unicorn managed to turn herself into an alicorn, after Celestia's careful tutelage. I'd think that this sort of magic could cause problems, if it fell into the wrong hooves...perhaps a certain tyrant king attempted to recreate the spells himself, and thus forced himself into an existence of smoke and stone...
MLP (c) Hasbro