Every power had its limits. Merlin knew this without needing Gaius' interminable lectures about the balance of the world. It was practically self-evident: kingdoms rose and fell, rivers changed their courses, mountains were worn away by the ceaseless caress of the sea. It was easy to know that, but harder to believe it when all the magic in the world (or so it seemed) was crashing through him.
The river that ran below Camelot, that fed her cisterns and emerged into the sun on the eastern edge of the city, was more than a river. Merlin had felt its song the first time he dipped a hand into its steady current. It followed a course carved by the ponderous cycles of the earth itself, cycles so long that they were practically imperceptible to mortals. But if one were patient and listened, it was almost as though a great engine lay far below the feet of men, some ancient and implacable contrivance of the gods themselves.
Merlin had used this in small ways when he placed the city's defenses, but his instincts had urged caution. There were depths of power there that simply could not be harnessed, any more than one could leash lightning.
But that is what he did.
His fall from the city wall became a plunge into those slow-moving currents of power. He had hoped to pull Morgana's summoning with him, to envelope it and destroy it, but that would not be possible now. Instead, he used the conduits of his own magic to divert that river. It burst its banks in a barely controlled flood that obliterated the dark, amorphous creature as easily as swatting a fly.
Yet as quickly as the task was accomplished, it was forgotten. For one frozen, eternal moment, Merlin rode the crest of that wave. All the kingdoms of the earth lay before him: pebbles ready to be crushed, a skinny boy from Ealdor the only obstacle between them and the raging flood that screamed to be released.
Nothing would stop it. Nothing could. And for the barest of moments, he couldn't think of a reason to.
But Arthur was on the battlements, blood chasing terror through his veins. Gwaine stood nearby, sword singing with battle readiness despite the darkness through which they had passed. And behind them were all the people of the city, from stableboys to nobles, hope and fear warring for their souls. Every one of them was a tiny, guttering flame, so small and fragile that the most distant whisper would snuff it out.
Merlin began shutting the doors of his mind in a terrified rush, trying to force the surge of magic back down, but it was like trying to stop his blood from flowing. He remained the weak point in the world, a hole through which the breath of the earth could escape. He was built to channel magic, to make himself a part of it and shape it as it shaped him. He was of a kind with that power, and it sought him out like an arrow seeking its target. If he let it find him, it wouldn't matter that he had saved Camelot; he would doom the world.
His blood was fire, his breath a storm. He chased those currents of power and scattered them, tearing them apart before they found their way into the world. He couldn't tell whether he himself was falling or whether the ground was rising around him, obscuring his awareness until there was nothing left but that ponderous, eternal rhythm measuring out the aeons.