When Merlin first realized he stopped aging, he thanked his lucky stars that he had at least made it past puberty.
He thanked them again that he knew enough aging potions and spells to keep anyone from becoming suspicious.
He cursed them when everyone he knew grew old and died, leaving him alone.
One generation. Two. Thee. Ten. Fifty. He stopped counting.
Merlin sometimes envied the mortals for their short memories just as much as for their short lifespans. After centuries of keeping up with current events, certain the next disaster would be the time of "Albion's greatest need" and thus Arthur's return, Merlin had seen far too many horrors.
But he could not forget. He must keep remembering. Because if he began forgetting, Merlin feared he would forget everything. He could not afford to forget why he was here.
So every day, Merlin wrote down what was happening to him and to the world. And every day, he read a year's worth of journal pages. He has a wall of bookshelves dedicated to these history books.
The deaths of Arthur, Gwain, Morgana, and Mordred were just the beginning. He'd born witness to England's greatest triumphs and tragedies.
The fall of his beloved Camelot
Wars with the Saxons, the Vikings, the French, the royals, the non-believers
The Black Death spreading like a curse upon the land
Arthur, Prince of Wales (who Merlin had hopes for) dies young
Witch hunts (Merlin was horrified by the return of the Great Purge)
The international slave trade
The rise and fall of the British Empire
The World Wars
And worst of all- the world stopped believing in magic. He almost preferred the time when they feared it. At least then people had still believed he and his kind existed.
At least then his kind had still existed.
Merlin sometimes envied the mortals for their short memories. He won't ever forget; he won't allow himself to forget what it is he waits for.