So, this was published on 02-11-13 but for some weird reason I placed it under the Merlin archive- not the HP & Merlin crossover. Today I decided that not having it here was kind of just missing the point. :)

(This was the first thing that popped into my head after the finale.)

"[ The mirror of Erised] shows us nothing more or less than the deepest, most desperate desires of our hearts."

- Albus Dumbledore.

.

Descend, and touch, and enter; hear
The wish too strong for words to name;
That in this blindness of the frame
My Ghost may feel that thine is near.
-Tennyson.

Tell Me Now.

When he'd been a young boy in Camelot Merlin could not see the reason for Uther's rage. He could see a man broken and lost but yet the hatred that pooled inside those eyes whenever magic was as much as mentioned had puzzled the young warlock.

Now, old and ancient though his skin remained as taut as it always had been, Merlin understood.

It had taken a man named Lord Voldemort so that he could see what Uther Pendragon had seen and his blood recoiled in horror as his kind was tortured and murdered by the thousands. He'd tried to take matters into his own hands once only to find that the demon could not die.

He'd shivered at the ineptitude he saw when the Ministry of Magic did nothing to alleviate his kin, as terrified of the monster as only cowards would be. He'd howled and screamed in rage and his eyes- for the first time in centuries- had flashed gold as his magic lashed out and yet those cold men did not yield and not for the first time he suspected something as ancient as the Fomorroh was controlling all of their minds. (1)

He vowed that he would stop the carnage, no matter what it took or how lonely he would be, and he hunt the demon down. Of course, his attempts brought attention over him and it wasn't long until those dark wizards had tried to restrain him with their magic, tried to kill The Emrys in defense of their Dark Lord.

As if Merlin would let himself die when Arthur needed him.

They'd left him for dead and since that moment The Emrys had cloaked himself in mystery. Many few men knew of his existence and even fewer knew his real name.

He was no longer Merlin, the Merlin that Arthur would pronounce so distinctly in that way of his that used to make him chuckle quietly when he was a young serving boy and that now, whenever it echoed from his memories, made his heart ache. He'd had a variety of names, some of which humanity would forever recall, others which helped him walk unnoticed through the streets of that land that he and Arthur had built together.

Now he was Emrys, forever young and all-powerful. Yet not even his great power could do much against the hoards of witches and wizards that killed in that reign of terror.

That didn't mean he hadn't tried. And the rumors of the great man that acted as a guardian angel upon them all soon spread through the wizard community. He made his way through the darkest of times trying to alleviate the suffering as he could while keeping himself hidden.

In those days he often wondered if Uther Pendragon was rolling in his grave.

And what would Arthur say? He could almost picture his King perfectly if he closed his eyes and stood still and silent, letting an onslaught of memories wash over him. Arthur would urge him to fight on for what he knew to be right.

He could almost feel Arthur's whisper. 'feoht' (2)

And so he did because Arthur's voice- even if he was imagining it- always brought him courage. He fought for his kind, no matter if they were magical or not. Those loyal to The Dark Lord found their plans thwarted by a cloaked figure that struck terror into their very souls with its golden eyes and guttural voice. He was a shadow, a ghost in the dark, a savior to many and an acquaintance to none. Perhaps, Merlin thought, it was because of the unusual practice he'd gotten in Camelot, that he managed to keep his real identity secret and his face unknown. He was as ethereal as the shadows vanishing in the morning light.

That's why he was surprised at seeing a letter certainly directed to him, (or what was his name at the time) when he thought no-one knew he existed. The letter was folded neatly on the small coffee table near Merlin's favorite chair (one he'd gotten in the sixteenth century) and it read.

Dear Mr. Thomas:

If it is convenient for you I shall visit you during this Thursday afternoon to discuss matters that, I am afraid, can be resolved only by your assistance. I should be glad to offer you a bottle of Madame's Rosmerta's excellent Butterbeer. I hope to find you in good health,

Albus Dumbledore.

And so, with the same curiosity that made him try that strange drink called chocolate once and that Gaius had- in his treasured memories of Camelot- often complained about, Merlin hadn't moved an inch since noon. He tapped his fingers against the armchair as he waited, wondering how on earth would-

Poof!

His old chimney was suddenly engulfed in emerald flames and Merlin thought for one heart stopping second of Morgana and her tainted magic although it had been decades since the thought of the witch had crossed his mind. However he only had a second to tense his body as his heart began racing before all of his fears were proven false.

"Ah!" said a man who'd just taken a step towards his Arabian rug and who had, apparently, appeared in those green flames. He adjusted his glasses upon his nose. "I'm sorry about that. Sometimes I prefer flu than apparition though I always end up regretting it." almost absently he shook dust from his robes. "But one hardly learns from past mistakes…though we should try."

Merlin, perhaps for once rendered completely speechless, just stared at him.

"You must be James Thomas then!" said the strange visitor, smiling as if Merlin was a long lost friend. "It's a pleasure to meet you, I assure you."

Before Merlin knew what was happening the man was shaking his hand enthusiastically and patting his shoulder with that sincere smile still on his face. Many times throughout the years Merlin had seen people trying to imitate him – though they never knew that the great wizard with a soft white beard and staff was nothing but what he'd been in the battle of Camlann and what had forever stayed in the minds of the those who later told the story, they never knew that Merlin had been once young and beardless with a face that spoke of the highest loyalty and devotion- but this man, this Albus Dumbledore certainly was the greatest imitator yet. His long silvery beard and piercing blue eyes reminded Merlin so much of Dragoon the Great that it made his heart shudder.

"You are Albus Dumbledore."

The man hummed and nodded, taking one long wooden stick from his robes and waving it, two bottles appeared out of thin air.

"Yes I am." The man agreed, "I'm sorry, I'm being terribly inconsiderate. Could I take a seat?"

After Merlin had given his consent Albus Dumbledore sat down in a worn Morris chair that dated back to the seventeenth century. With piercing blue eyes and a kind smile he uncorked the Butterbeer.

"We've been searching far and wide for you Mr. Thomas." Albus Dumbledore said as he poured the liquid from the bottles into glasses that his robe shouldn't have been able to contain and offered one to Merlin. The ancient warlock took it, still trying to form a coherent thought.

"You- you are not from that blasted Ministry, are you?" Merlin said finally, feeling his brows almost touch as he frowned and his nose crinkled.

Albus Dumbledore's beard tugged upwards and Merlin was certain that he was smiling. "No, I'm not." and then, with the simplicity one would ask for a cup of sugar, he said. "Actually, Mr. Thomas, I come on my own on behalf of an old friend. We need desperately the service of a Dragonlord."

When the word echoed in the small house, bringing with it memories of a long lost life, the warm fire coming from the chimney flickered and stuttered Merlin was so startled that the glass he held fell to the floor and, as his eyes sharped and fixed on Dumbledore, he could almost feel the dormant ability inside of him crawling and waking.

Dumbledore said not a word as Merlin knelt down and picked up the broken glass. He did not urge the tall, soft-spoken man to use magic. He just watched. Finally, from his place knelt by the fire place, Merlin raised his gaze. "I haven't heard that in such a long time." said he. "I thought I never would hear it again."

He tried not to let his thoughts wonder. Because he would, of course, remember past conversations and Kilgarrah, and then, as inevitable and as overwhelming as the light of the sun, Arthur would crawl his way back into his mind and with him all the sheer agony that he tried to repress each second of each and every day.

"We feared they were all extinct." Dumbledore said and if he saw the trembling of Merlin's hands he pretended not to notice. "But then we learned of you, Mr. Thomas."

"How?" Merlin's voice was harsher than he intended but he, frankly, did not care. While he was still picking the shards of glass from his Arabian rug Dumbledore paused, as if considering, before continuing, softer than before.

"Such power cannot be hidden forever, my young friend... Reparo."

The shards in Merlin's hands knit themselves together in less than what it took a heart to beat and a wrinkled hand took all of the warlock's vision when Dumbledore leaned over him and helped him stand. "Now," the old man said kindly. "I would like you to come with me."

"Where?"

"To the outskirts of Scotland," answered Albus Dumbledore with a twinkle in his kind eyes, "There are children there, Mr. Thomas, that need protection from the dark forces that have been let loose around our world."

And Merlin wondered if this man, for all his smiling and kindness, knew who he was. If he was, indeed, part of the that ministry that was as cowardly as Uther once was because there had never been one time in which he'd say no to children in need. Not in all his years wandering the world without his King.

"I assure you..." said Albus Dumbledore softly and Merlin raised his gaze to find the man's piercing eyes burning holes into his. "I do not intend any harm, Mr. Thomas. You can trust me."

Merlin, with a heart hardened by years of pain without end, wars and famines, and a soul torn open by a wound that would never heal, found that his eyes were softening as the man spoke. Because there was kindness and honesty within his heart, a heart that reminded him of Guinevere.

"Yes," he said, without even realizing that he was saying it out-loud, "Alright."

Albus Dumbledore smiled and clapped his hands and the worn travel-cloak that hanged from an ancient coat hanger placed itself neatly over Merlin's shoulders. With a thin smile on his lips the warlock turned towards Dumbledore.

"How?"

"By Side-Along apparition!" Dumbledore said joyfully. "You must hold my arm tight. However, if your legs turn to jelly you must tell me immediately-"

"...Um. What?"

But he and Albus Dumbledore were already sucked into the night.

...

When the wind finally kept still long enough for him to breathe, Merlin found his feet were firmly planted on dewy grass and his hands shaking though he didn't know why. By his side, the tall and reassurance presence of Albus Dumbledore made itself known when the man placed a strong hand on the warlock's shoulder.

"Here we are, Mr. Thomas." he said. "This is Hogwarts School of Witchcraft and Wizardry."

And before Merlin's eyes there was suddenly a lake and a castle that brought back memories of Camelot's palace and loud laughter, of a prince and a manservant walking together through the sunlit corridors. He swallowed but could not look away.

"There are children inside those walls." Dumbledore said softly, "And Voldemort has targeted most of them, even if they are young souls that have done no wrong."

Only the winter wind whistled upon the hills when Merlin did not answer. But the coldness in his eyes, far greater than the one that had been there during the World Wars, said what a thousand words could not.

"We know Voldemort has dragons between his allies and if all of these innocent lives are to be defended...Mr. Thomas, we need a dragon as well."

They had no need of him, not really. Merlin knew that. These dragons were not the magical beast he had known, they had evolved and eventually became only empty shells of what they had once been. None of them could conjure magic as ancient as time and spin riddles. None of them had the gift of prophecy and none of them sought him by name as Kilgarrah once did.

But he did it anyway.

A dragon egg was a rare find, Dumbledore said, and Voldemort had the loyalty of most of the dragons and their off-springs as well. So when he had acquired a egg-shaped rock that happened to be a dragon egg there was nothing else in his mind than the need to hatch the creature.

But the egg could not be hatched.

And so it fell unto Merlin to try and use his long-forgotten tongue so that the ancient creature would see the light. It happened right beside a forest and centaurs, hidden behind the shade of the trees, stood and watched. With a roar that came from the deepest part of his soul Merlin called for the dragon and gave it a name and then a cry broke the stillness of the night.

If Dumbledore and the tight-lipped woman by his side noticed how James Thomas' eyes swirled with gold they said not a word.

(Merlin never knew it but, later on, that same dragon he'd hatched and named Cathascach (3) saved three young wizards by breaking through the glass-ceiling of a Bank.)

On that same night the sky darkened and the ceiling trembled.

At Merlin's inquisitive look Dumbledore simply answered, "If there is one thing that Voldemort cannot conceive it is defeat. He won't stop trying to take Hogwarts. And I fear that, one day, he might find a way to fool us."

There were children in that castle. There were young men and women with lives ahead of them, lives that would be crushed in an instant if Voldemort ever managed to penetrate the defenses that kept the darkness at bay. For the first time in a thousand years Merlin held out his hand and looked directly into the eyes of Albus Dumbledore as he said, "Let me help you. I can fortify the spells around the school. I can make them stronger."

The man nodded and Merlin turned as he chanted. Invisible tendrils of golden magic shivered in the air and surrounded the sleeping children that lay, unaware, in their beds. Albus Dumbledore looked on and when Merlin turned with a paler face and brighter eyes he walked towards the legendary warlock and said, "Come on, Mr. Thomas. I think we both need a cup of tea."

But the warlock Emrys shook his head. There was far too much to do and he could not- would not- waste time in something as trivial as a cup of tea. With a sad smile and a glance at the gold and bronze ceiling the warlock asked Dumbledore to show him 'every last remnant of the castle so that he could extend the enchantments upon everything and everyone.'

When Dumbledore had fulfilled his request at the best of his capability and the ancient words of the Old Tongue were whispered upon the library and the east wing, the highest towers and the open grounds, there was hardly any space that hadn't been touched by The Emrys' magic. For years without end, that same legendary essence of Merlin would make Hogwarts one of the safest places on Britain.

But, as Albus Dumbledore would one day tell the tight-lipped teacher that was Professor McGonagall, Merlin still had one more room to open, one more chamber to bless with his presence.

The mirror was there, in the corner of the bare room, almost as if it was waiting, almost as if it was glad. As he chanted and touched with his forever-young hands the stone walls of the chambers, Merlin did not even notice it.

He stopped only when he caught part of his reflection on the mirror and saw the tired, sad eyes of a man that had lived a thousand lives and perhaps he only wanted to narrow his eyes at the discordance that they were, an anomaly, for his face was as young and as handsome as it ever was and his eyes- those old, tired pupils- had lived and died ( not only death could kill. ) a thousand times. Sometimes, he wondered if other people could notice it too.

But then he saw- instead of his haggard and pale face- something else entirely.

Yes, he saw himself. He saw a tall, lean man with black unmanageable hair and eyes that spoke of a tragedy far greater than what anyone could imagine. He saw the worn cloak that he'd bought during the fifteenth century and his lips, trembling as they formed a name he hardly dared to say out loud because it only represented false and cruel, heart-stopping hope-

It was him.

There he was and Merlin could not stop himself when, with a cry that he muffled with his hand, he let the name slip past his lips and linger in the air,

"Arthur?"

And the glorious apparition at the other side of the mirror nodded and mouthed carefully 'Merlin' as if he, too, wanted to reach through the glass and touch his warlock. But instead he settled for placing one arm around Merlin's reflection and squeeze, almost too hard if it had been real, Merlin's shoulder.

Arthur looked at him with sorrowful eyes and his lips formed the word again, 'Merlin.'

The warlock muffled a sob and suddenly he no longer cared about Dumbledore standing silently behind him, he no longer cared if his secret was finally revealed and the Dark Lord hunted him for this was Arthur and he was calling him and Merlin had not seen him in thousands of years and now- for the very first time since Camlann- he had set his sight upon that which was most precious to him.

How many times had he closed his eyes and squeezed them until it hurt just so that he could picture Arthur again, awake him from his memories, so that his King's face would act as a light upon the darkness of the trenches, as a beacon in the carnage that was war and famine and witch hunts...

He'd been so afraid that time would erase his recollection of Arthur. That his memory would eventually fail him and he would never again remember the way he laughed, the mischievous twinkle in his eyes, the clumsy way his King would ruffle Merlin's hair and the way he frowned when something worried his noble heart...

Yet here he was and he was as young and strong as Merlin remembered him and there was not one detail that Merlin hadn't guarded within his heart. He walked forwards, barely daring to hope that it was real- and his fingertips brushed the cold, cruel glass.

The arm that was around Merlin's shoulder tightened and the warlock choked a sob when he felt nothing, not even a gust of wind, around him. But soon Arthur raised his own hand- the right one, with the scar in his forefinger, Merlin realized- and touched his own fingertips where Merlin's were pressing the glass so hard that it was a wonder it had not broken.

"Arthur, Arthur..."

He felt hot tears spill from his eyes as he blabbered the name. And as soon as he knees gave out and he knelt on the cobblestones Arthur fell by his side, looking at him with pity and a tenderness that Merlin had never seen in his eyes. He mouthed something again and even if Merlin could not hear it he nodded, for he knew Arthur was asking him to be strong.

Feoht.

"ic cunnan, mín aldfriþ." (4) he answered quietly, so softly that he barely heard it. But his King smiled and his eyes twinkled from the other side of the mirror and Merlin knew that, somehow, Arthur had seen what was in his heart.

It was then when it occurred to him and his soul shuddered with a joy that left him paralyzed for the smallest of moments before he pressed both palms to the cold glass and closed his eyes- therefore not seeing the way Arthur did the same and looked at him with the deepest sadness before he bowed his golden head.

But the hope that had sprung within Merlin and rooted itself in the briefest of assurances was roaring inside him, a roar that soon became a stream of words from the Ancient Tongue as his eyes burned with the strength of a thousand suns and he tried to break the fragile barrier between them, to dissolve the glass that kept The Emrys and The Once and Future King apart.

Yet, the glass remained unyielding.

"No..." when he looked again at the reflection, inches away from it's surface, he found Arthur's eyes locked with his own and though he did nothing but look at him Merlin knew that all of his powers- all of his talents- were worth nothing. Nothing, because Arthur could not return to him.

"No!"

"It is of no use, Merlin."

The hand upon his shoulder was not Arthur's even though his King was still clutching him in a vice-like grip on the other side of the mirror. Albus Dumbledore knelt before him, real and solid, and spoke with a softness that reminded Merlin of Gaius, "What you see here it's not real, dear boy. You cannot do anything."

Not even realizing that Dumbledore had used his name in his pain, Merlin pressed a hand to his lips, "Please don't- There must be...I have to..."

"This mirror, " continued Dumbledore, relentless. "is The Mirror of Erised. Erised stra ehru oyt ube cafru oyt on wohs. It is as dangerous as it is uncommon. What you see here is only the most desperate desire of your heart, dear boy."

Swallowing the tears that burned his throat though they still fell down his cheeks, Merlin whispered, "Arthur..."

He turned his head so that he could look at Dumbledore and found that the man's eyes were glimmering though he didn't dare to think they were tears. "I understand, Merlin."

"You don't..." The Emrys whispered sorrowfully. "No one can."

"It is true, that the legends refer to you as 'two sides of the same coin.'" said Dumbledore gently, piercing with his gaze Merlin's gaunt face. "And perhaps I know not what it feels like to be entwined as you are but I've known loss and death and I know what it is like to live without what is most precious to you."

As if he knew how true his words were, Albus Dumbledore said nothing more. He placed both arms around Merlin's young form and let the man cry silently for he knew that maybe Merlin hadn't done so for thousands of years.

"How do you know my name? " asked Merlin finally, once his shaking shoulders had stilled and his hands stopped trembling. A warm smile answered him as Dumbledore's beard tugged upwards.

"The golden eyes were not as subtle as you would like to believe." he said gently, " Besides, I am certain that Geoffrey of Monmouth recorded Merlin as the last of the Dragonlord in one of his letters. People sometimes dwell in the wrong details...and forget to look into the important ones." his hand squeezed Merlin's shoulder with the touch of a father. " Your face may not be old as some legends say Merlin but your eyes speak of your grief."

Merlin bowed his head as the man spoke. He'd never met anyone that could see the never-ending centuries written on his eyes. He knew he was still young-looking and handsome, that was why most people did not look beyond the smooth skin and into the grief-filled eyes that told everything.

"I've waited for years without end." he admitted, never-once looking away from Arthur's reflection, whose eyes resembled Merlin's very own. "I've waited for him and I've done so gladly. But now...I just don't know what to do anymore."

"This was not in vain, was it, my dear boy?" said Dumbledore, "All of these years you've benefited us, wizards and muggles alike, in ways that could not be possible. Don't you see? Today, thousand of children will dream without fear because of you. In centuries past, many innocent men and women were saved from a cruel death thanks to your courage. Your wait holds a purpose, Merlin. You must not forget that."

'courage'

Arthur's grinning face flashed before him and with him the memory of a small man, a dear friend and a bridge.

"I've waited so long..." he murmured, wiping his tears. "I'm tired...I am so tired..."

"I have faith." said Dumbledore, handing him a patterned handkerchief. "that the Once and Future King will rise again. You must hold on to that knowledge, Merlin. Sometimes, it is our only light in the middle of our darkness."

Merlin raised his eyes and the hope that he saw in Dumbledore's made his heart beat faster for he knew- perhaps even more so than him- that Arthur would return to his warlock once again, when the time was propice.

When he glanced once again at the was his heart's most desperate desire, Merlin smiled.

"I'll see you again, old friend." he whispered as he pressed his forehead to the cold glass and Arthur bowed his head over his from the other side. "I'll see you again, mín broðor. (5) I'll wait for you."

And he did.

(1) Merlin's not that far from the truth. They were controlled by the Imperius curse, actually.

(2) fight in Old English.

(3) Irish name that means 'vigilant.'

(4) Old English. "I know, My King."

(5) My brother.