A/N: Well, here's my attempt at a Harry Potter/Merlin crossover! In my opinion these two fandoms complement each other amazingly well, and I've always been so frustrated at the lack of good fan fictions for them. With an exception of a very few, they seem to be all vastly OOC for one or other of the set of characters. So, I've decided to write my own, and I hope I can do justice to both of these great fandoms! Enjoy!

Disclaimer: I do not own Merlin or Harry Potter … no matter how much I want to.

AU from the chapter 'The Battle of Hogwarts' in Deathly Hallows. Written after Series 4 of Merlin but before Series 5, so everything that happened in the last series does not affect this fic.

He had always known this moment would come. It was inevitable really. He'd been on this earth too long to attribute his continued existence to a mere accident. There was a reason he'd survived this long, he'd had plenty of time to ponder that fact, and now the frustrations of the centuries he'd endured, and the patience he'd exhibited was about to come to its end.

It was strange really. He'd spent so long waiting for the moment when he'd once again emerge from the shadows that he'd never really contemplated what he might do when that day came.

That the day had come he had no doubt, he couldn't explain how he knew, he just did. And it couldn't have come sooner.

He'd never interfered, no matter how much he'd wanted to, no matter how desperately he'd wished could. He had no right to interfere in the modern day world; it was not his place. His place had been in Camelot, with Arthur and the others, a place where the Old Religion was rife, where its power had surged through every living thing and brought peace and harmony to the world.

But that world had gone now. After Arthur's death, more than thirteen hundred years ago, the magic of the Old Religion had fallen into decline. Everything he'd worked towards during Arthur's reign was suddenly destroyed by a single act. Mordred, the once innocent child, had slain Arthur on the field at Camlann, and with that, the balance of the world had been destroyed. The Old Religion had cried out at the atrocity, and its power faded. Its legacy had been kept alive for only a few generations, before ultimately, it was forgotten and its knowledge was lost.

But not completely. He was all that was left of the old ways. He had lingered on, the power of the Old Religion still running through his veins, the last relic of all that had been good.

He felt it still, even after all these years, as strong as it ever was. It guided him.

He had always refused to believe that the power of the Old Religion was totally eradicated. He sensed it still; it was all around him. Even the Muggles felt its presence, though less attuned to its inherent power. It was hibernating, resting until the wrongs that had been committed all those years ago could be righted. Only then would it truly return.

Yes, the Old Religion was still out there, he was sure of it.

It had been incredibly frustrating, in the centuries after Arthur's death, to see how truly lost it had become. Lesser magic had replaced it, simple buffoons wielding 'magic sticks', who in the old days, would have been dismissed as simple magicians suddenly rose to prominence, and became the new form of power. He had been scornful at best, and even though throughout the centuries their magic and powers had come far, it had never come anywhere near to his own. His and his alone, was the true magic.

He had watched over the years as their society developed, often amused at their antics and their inability to project magic through any other means than through a piece of wood. None of them had harboured any real power.

Then, about a thousand years ago, four young users of magic had come to his attention. They had used wands, like the rest of their kind, but unlike the rest, the power they had harnessed was something he had not seen since his own youth. What he had seen was an amalgamation of the Old Ways and the New. They had been exceptionally powerful, and he had known that this was one of those rare occasions he could intervene. They had an idea, a crazy idea it had seemed at first, to build a school far from Muggle eyes, to instruct young users of magic.

He had been intrigued; a school such as this would certainly have made his youth in Camelot a whole lot easier. Yet at the same time, he'd been hesitant. To make magic accessible to the masses, while admirable, seemed to him to be lessening its mystique. He remembered himself the wonder and amazement at his own discoveries using magic, of pushing himself as far as he could to become the very best, to discern for himself the essence of pure magic, and this school seemed to disregard it. In his opinion, it had made magic a right, and not a privilege.

Yet, he'd come around in the end. The Old Religion had granted these four Founders extraordinary power, and he knew it must have been for a reason. It wanted this to happen.

So he'd helped them, giving them advice, teaching them of magic they could never have dreamed of, never revealing his true self and watching as Hogwarts flourished.

His earlier apprehensions had proven unfounded. It gave him more joy than he'd had in centuries to witness the young minds being expanded, and their powers cultivated and encouraged. So many children from Muggle families, who would otherwise have lived in fear of their strange abilities were given the chance to live a full and happy life with others of their own kind. It took them away from ignorant Muggles who feared they were 'possessed' and introduced them to magic in a way that taught them how to truly appreciate the wonder that it was. He'd hoped such education and sense of community would have led them on different paths to the one that had led Morgana to her destruction.

But, Dark Magic still prevailed. No matter the education, no matter how much was offered them, there were always those who considered themselves superior, and wanted more. And he had certainly witnessed much of that.

It pained him to watch such evil fester in the world and do nothing, but his instincts told him: now wasn't the time.

However, Hogwarts certainly brought more advantages than disadvantages. It showed young children that they had no need to fear their abilities; there was always a place for them. And it had torn him apart the day he had finally decided to leave, leave the new friends he had made, the only ones he had known since Arthur's death. And the Founders Four were soon scattered by abandonment and death, and people began to forget the new ideas they had brought and the amazing things they had done.

The witch hunts had been the most trying era of his life. Europe burned, witches, wizards and Muggles alike were slaughtered in their masses. He couldn't save everyone, even if the Old Religion had allowed him to. He almost lost faith in it; how could it let such atrocities occur? But he'd bided his time, painfully and despairingly, praying for an end.

It had been a sad day when the International Statute of Secrecy had been signed. He had resigned himself to the fact that it had been an inevitable conclusion to a world torn apart by hate, fear and violence, and that it truly had been the only way forward. Yet it still saddened him, and he couldn't help but long for the days back in Camelot, where sorcerers and Muggles lived side-by-side in peace and harmony in a mutually beneficial society. It drove him to despair to think that this was what his kind had been reduced to. Hiding and skulking in the shadows, afraid to show their true colours. It reminded him forcibly of his own terror-ridden childhood. No one should have to live in secret, even if by choice.

Watching had become progressively harder over the centuries after that. Muggles began to forget about the truth of magic and wizards were content with hiding themselves away. The wish of the Founders to bring peace between Muggles and wizardkind through their school had been fulfilled, more or less, but not the way either they or Merlin had ever envisioned. Peace only existed because both sides were separated by years of ignorance. The integrated society that had strived for had never seemed so far away as it did now.

He'd kept an eye on things of course; he knew he had to wait for the day when he would once again come forward. He'd even attended Hogwarts a few times, both as a student, and as a teacher, casting simple spells to disguise his age and lack of a plausible backstory.

How amused he'd been when he'd first been Sorted. The poor hat had nearly fallen off his head in shock! In the end it had refused to Sort him, claiming he was not worthy enough to presume to understand magic of this power (he'd blushed profusely at this; he'd never gotten over his relative fame) and he'd ended up choosing his own House. He chose a different one every time (he needed a little variety in his life after all). His favourite by far had been Hufflepuff. As much as he admired bravery, intelligence and ambition, he felt a true measure of a man was to see who he was deep down. Loyalty, hard work and determination were qualities he felt were far too often overlooked and taken for granted; it didn't matter what other qualities they possessed, if they had these few, then that was all that was needed to prove themselves truly worthy in his eyes.

Besides, he'd never yet met an evil Hufflepuff.

He'd often thought Gwen would have been a Hufflepuff; she was just a truly good and honest woman who'd touched the hearts of so many, just by being true to herself. He often thought how well Gwen and Helga would have gotten along, so similar were their personalities and views. He amused himself sometimes by trying to Sort all of his old friends into Hogwarts Houses; Arthur and Gwaine reckless and courageous as they were into Gryffindor, Lancelot the ever-loyal into Hufflepuff, Gaius the scholar into Ravenclaw … before the sadness overcame him once more. They were all dead and gone, yet he still lingered …

His various times at the school had been amusing, a momentary distraction from the unending centuries. He'd become proficient in 'Modern Magic', even purchasing a wand, despite despising it. He hated channelling his magic through it; he always had to be careful to rein it back. His first time holding a wand and attempting a spell at Mr Ollivander's shop had been disastrous. He'd destroyed half the building trying to do a simple levitation. He never used his wand unless he could avoid it; it was too restrictive.

He'd excelled of course at Hogwarts, making sure he always knew the up-to-date versions of magic in the modern world to avoid awkward questions. Having to act the part of an ignorant child was frustrating however, and he never dared get too close to any one- he knew it would only cause him pain when they eventually succumbed to old age. The only ones he dared become openly friendly with were the ghosts. He had known the Grey Lady exceptionally well when she was just little Helena Ravenclaw and running around the castle chasing house-elves when he was helping her mother and the other Founders with the school. Seeing that happy little girl as a ghost for the first time had been incredibly painful, and he could never cease to be reminded of the happy times he had spent with her and the Founders whenever he saw her pale form drifting through the corridors. He had also met the other ghosts throughout the centuries and he could hardly avoid their company, however much he wished to in the case of the Bloody Baron. They knew he was more than he pretended to be, but they kept his secret. They and he both knew the pains of watching the modern world charge forward whilst remaining unchanged themselves. The portraits too, kept his secret- the Fat Lady in particular seemed to have a soft spot for him. Even Peeves kept silent, miraculously.

But it still pained him. He knew he could not interfere in the present world to any great degree; he sensed somehow that the Old Religion had forbidden it. He'd seen the visions centuries ago, when Morgana had lured him to the Crystal Cave to keep him from protecting Arthur at the fields of Camlann. He knew when he must come forward and that time had increasingly come closer within the last sixty or so years, with the birth of Tom Riddle.

He'd reminded him of Morgana a little, bitter at the world, and determined to punish everyone in it. He'd witnessed his rise to power, hating himself for not intervening. His time had been close, but not quite there.

He'd watched as he committed atrocious acts against magic, splitting his soul in a way too abhorrent to think about. Yet, he'd still waited.

He'd watched as Albus Dumbledore had attempted to fight against him, a futile attempt. Although Dumbledore was the first man he'd seen in centuries with power to even begin to rival his own, against that kind of evil, there could be no victory. At least for him.

Then, when all had seemed lost, he had been born. The one he'd waited for.

Harry Potter took his first breath.

He defeated Riddle whilst still an infant, and suffered cruelly because of him. He'd grown up hated and despised by his own family, gawped at wherever he went and forced to face unimaginable horrors from a young age. He had known deep inside of himself that Harry had been the one from the moment he had been born, and this was only confirmed when he defeated Riddle and was left with the scar the shape of lightning. The vision Helga had had so many years ago about the boy with the lightning scar was finally coming true after one thousand years of searching.

He'd grown impatient. He knew the time was closer than it had ever been. But he watched as Harry's years at Hogwarts had passed.

Then it had happened. Voldemort had returned.

He'd known it from the moment Voldemort had stepped from the cauldron. The Old Religion had cried out in a way it hadn't since the day Arthur was killed. This was just so wrong and abhorrent. Voldemort had used the ancient rituals of the Old Religion in such a grotesque way as to disrupt the entire balance of the world. Only Harry now had the power to stop him.

He'd told himself this was it, now was the time to come forward once more. But he held back, something hadn't felt quite right. He didn't reveal himself to the entire wizarding world. Instead, he'd gone to Dumbledore.

He'd been pleasantly surprised when he found out Dumbledore had already theorised about the existence of the Horcruxes; he too often forgot that although the wizarding world had not the same power as the Old Religion, it had still come far in its advances. He too often underestimated these people.

He hadn't revealed his true identity to Dumbledore; something had told him that was not the right move. But Dumbledore had been a powerful enough wizard to sense the power that came with his new acquaintance, and knew he was of the Old Religion, and so had trusted him implicitly- especially after his phoenix had openly displayed his own trust in a remarkable echo of the way Godric's own phoenix had done so a millennium before.

He'd dropped in every so often, to learn of Dumbledore's progress, urging him to reveal the prophecy to Harry, pointing him in the right direction, but was always careful not to step too far over the line. It was Harry's destiny to ultimately defeat Voldemort, and his own destiny to protect him while he fulfilled it. It brought certain pangs of sadness to his heart when he remembered another hot-headed youth who'd played a similar part in his life.

He himself knew everything about the Horcruxes, he could sense their evil presence in the world at all times, but he dared not reveal too much to the Headmaster. He was only here to guide, not to do everything himself. Harry was the only one who could do it.

It had riled him considerably to see what Harry had been forced to endure during his fifth and sixth years at Hogwarts, the place which should have been his safe haven. He'd urged Dumbledore again and again to reveal everything to Harry, everything he had a right to know, but Dumbledore hadn't listened. It had driven him almost to the point of insanity. Dumbledore respected him, even admired the strange man who popped in every so often with disturbingly accurate details about his most private affairs, but he still remained firm. He often wondered if Dumbledore would have been so stubborn if he'd known his true identity.

But, he remained largely hidden, even after Dumbledore's demise, when he thought Harry would have needed him most. He watched in silence as Harry and his friends took on the most difficult and dangerous quest anyone should have to endure. He was there every step of the way, through all the dark and harrowing times, invisible, never interfering, always listening to the instincts of the Old Religion: not yet, not yet …

They hunted down and destroyed the Horcruxes, and he felt himself become incredibly proud of the three teenagers who risked everything for each other, as well as extremely amused as he thought of the Founder's reactions if they'd learned what had become of their precious heirlooms. Helga's anger in particular would have been a joy and a terror to behold. Those objects had meant so much to them.

In what felt like no time at all, they were back at Hogwarts, rallying the other students to fight back against the evil that threatened the school whilst he remained in a corner, invisible and impatient.

He watched as the battle for Hogwarts began. He felt it as the cup was destroyed. Only three more left, yet the hardest one of all still loomed. He'd prayed to the powers of the Old Religion Harry would have the strength to do what was needed.

Then, all of a sudden, he knew. This was the time. It was a perfectly ordinary moment- he was standing in the corridors of Hogwarts wandering aimlessly as the battle raged on around him and he knew, now was the time.

He pulled his long under-used wand from his pocket and held it lightly in his hand. Why now of all times- right in the middle of a battle no less- the Old Religion would choose for him to come forward he had no idea, but he knew without a doubt it was time.

He strode off down the corridor of the seventh floor, his wand outstretched. Be careful Emrys, the Old Religion seemed to say, it is your destiny to ensure the Old Religion is restored to the world. Protect the boy at all costs. He is the only one who can right the wrong that was done to the world thirteen hundred years ago. Only he can lift the darkness.

He smiled: "I will not fail." And he hurried off to join the battle.

Merlin Emrys had re-joined the world at last.

A/N: Please let me know what you think! :)