In one of those oddities of language, little ponies use the word "stable" generally for two purposes- one for stability, and the second for politics. Literally, a "stable" is a place where any pony can have a firm, equal footing- in legal terms, namely as a place of governance.
The Canterlot Stables then tend to surprise most tourists expecting hay-covered floors and perhaps a few cows, as they represent both the elected and hereditary center of the Equestrian legislature, serving the esteemed and most honorable Diarchs of the Kingdom of Equestria. That is, the milling and energetic course of the House of Commons, and it's equal in number but inherited-by-title positions of the House of Lords (despite being plentifully studded with Ladies in the modern era, most of the original House had been military, stallions, and the founders of a bastion of political tradition, and buck political correctness- even some of the mares preferred "Lord, sixteenth in their line of Lords" to presuming to break the chain with a mere "Lady".).
For every titled mare or stallion, an elected pony of the land (or rarely, another species), and through oft-raucous caucus and the best spirit of compromise, churned out an endless stream of laws for the Princesses to sign and thus keep the nation in balance and harmony- literally, Stable. Designed with pegasus construction, built with marble and limestone quarried by earth ponies and decorated with precision by unicorns, the whole arrangement of comfortably-sized yet cheek-to-cheek alcoves a random checkerboard of cloud-seat, 'corn-cushion, or a more sturdy arrangement for the hindquarters of a earth pony, all sparsely decorated and surprisingly simple, split into six sections (dating back to when the Stables were strictly arranged by race) that surrounded a broad stone circle at the center, half sun, half moon.
Every alcove was filled. Six rather nervous ponies stood in the center, to the loud and chaos-strewn cries that flew over their heads as six-hundred-and-sixty of their peers warmed up. Above them all, Celestia and Luna sat in a resplendently decadent balcony, four pegasi guards keeping a careful watch for wads of stray paper or perhaps a quill tossed in anger that found itself misdirected to the heights (or, in one infamous incident, a banana that had nearly coated the Celestial Crown in treasonous pulp). Celestia sat, looking decidedly dimmed and ragged, while Luna's mane had taken on a positively stormy sheen, which matched her mood perfectly. Their faces were veiled with black, and the mourning-lace could be seen spotting nooks in every direction as loyal subjects shared in their grief.
Prince Blueblood, Lord Of The Canterlot Seat was not one of them, and he was indeed cheerfully polishing an imagined smudge off his working desk, energetically arranging a stack of papers, and had even set a small vase full of tiger lilies up in one corner for good measure. The six ponies, themselves surrounded in their circle by three times their number in guards watched him with a mix of looks, none kindly, but all were kept silent. Rainbow Dash's mouth formed more than one soap-worthy word anyway in the unicorn's direction, and though Blueblood clearly saw it, he only grew more cheerful each time the pegasus scowled and made a nasty face, then waved a friendly hoof at the furious mare after a few of her more naughty lip-contortions.
Dash slid to the floor and sulked, exposing Fluttershy, who had been hiding in the center. She squeezed in turn behind Trixie and Rarity, snuggling under the cushioned and ebon-ribboned saddles each of them wore. Wordlessly, the two gently pushed their hips together and flank-hugged the shivering pegasus- who hadn't stopped shaking since they'd led them out of the prison cells and into the open. Some ponies had taken a very specific pleasure in screaming "MURDERER!" at the wing-hobbled creature, as each accusation had struck her like a sharp rock in the withers before the six had been loaded into a carriage and spirited through the streets to the Stables.
The only comfort they had was each other. At best, the guards were formally polite, worst cold and almost ready to pounce if one of them had stumbled into "trying to escape". Their families had not been allowed to visit, nor had even the Princesses been given more than the most formal of visiting time spent, with dour-faced government chaperones in a well-dressed cloud of official doom hovering near in every direction.
A gavel pounded out a staccato tap that the chamber's walls reflected into a TOK TOK TOK. The sound settled the legislature into a mild burble of restrained whispers, and their heads turned to a raised podium set opposite to the Princesses' seats. A mare with a golden-bugle cutie mark stood below and raised her voice:
"OYEZ! OYEZ! THIS MEETING OF THE HOUSES OF EQUESTRIA IS CONVENED, THE RIGHT HONORABLE LADY UNION ROSE PRESIDING!"
The red pinto mare shook out her mane a bit and set the gavel aside. With the cultured tones of a Bittish with excellent breeding, she set the charges out like rows of ordinance, ready to explode and neatly tailored to the utter ruin of whatever poor ponies happened to have them dropped on their heads. The only one to be relatively short-stinted was Trixie, whose offenses only extended to the final charges of "participating in mystical acts that led to the demise of a pony of noble standing", and finally ended:
"...regis filia Celestia, regis filia Luna, non potest dici."
For even of such acts, even if the Princesses themselves were involved, by law they were not spoken of unless the unheard-of act of impeaching the royal station was required (a law that had stood for over a thousand years and even at occasional urgings from the Princesses to use on THEM, never put to use.)
"We call the first witness to these accused acts before the Houses...", and a sapphire-sparkling crystal pony with bitter eyes was escorted to a post, where she began a barrage of words that covered five of the accused in shame and horror, and Trixie herself to shudder more than once despite having witnessed much of it personally.
Many of the witnesses bore bandages covering burns. Some, including one stallion chose not to cover them all, letting the wounds speak as much as their tongues did of the day. By the second witness, Fluttershy was hiccuping and unable to stand. By the fourth, Rarity joined her on the floor. The half-grown colt who stared blindly out as he recited the last thing he saw...
"And the nice pink pony that gave me a balloon the first day? She looked down at me all flyin' in the air, then I couldn't see no more."
...Pinkie didn't so much cry as she became the source of a new river in the Stables, one that could have easily cleaned the floor had it not been redirected to the seapony-decor fountain outside the chambers. And it continued, mercifully, for only a mere four hours, sixteen witnesses, fifteen minutes a piece. At that, the accused were allowed to give their defense.
Without Twilight, that was less than an eloquent one, and half of the accused were beyond doing much more than obvious and complete remorse.
"We...we were in these crazy glowing gem things! It wasn't us...well, it was us but we wasn't us in us so it WASN'T US! NO PONY WOULD DO THOSE THINGS! NO PONY! I'm...I'm a good pony...I'm a good pony!", Rainbow Dash managed to get out past chattering teeth- and then seized briefly, turning one side of her face into a rictus of bared teeth and causing the representative from Hoofington to faint from the sight. Sinking to her knees, the pegasus put her hooves over her aching head and silently begged it to just stop...
"We ain't no pony-killin monsters! We done fought monsters, we even kilt some...but...I ain't no pony-killer! That ain't me...it CAIN'T BE ME!", Applejack finally began to scream. "AIN'T NO APPLE IN HER RIGHT MIND WHAT'D DO SUCH A THING! IT AIN'T ME, AND IT AIN'T MY FRIENDS AND I DON'T CARE NONE WHO SAYS IT WAS! THEY AIN'T KILLED NO PON-"
A winged shadow grew over the cluster of prisoners as a collective gasp rocked the assembly.
Princess Celestia settled to the House floor within the circle of the accused and raised her head. Her mane fell limply and nearly without life, like a flag on a broken standard, and her eyes were tinged with the colors of a bloody sunset.
"Enough. The deaths and pain of these little ponies was not theirs, and I will see them tortured no more by this trial."
"M-majesty!", Union Rose spoke from her lofty perch. "The law states that royalty shall NOT stand with accused or defender, lest the law be biased by your favor!"
"The Throne IS the accused, madam Speaker.", Celestia replied. "The witnesses have spoken truly to the acts they have witnessed, but they could not, neigh should not have known what stood behind them. It was..."
The time for a single breath was all it took to have every eye fixed upon Celestia's lips.
...it was me. What I have wrought in the name of Harmony turned upon it's bearers, and the fault is mine. It has been twice mine, and I will confess it before my little ponies, and judge me true for my works. I took a spirit of great power and bound it's sixfold parts into the Elements, and with my Sister unknowing, we did usurp this spirit's powers to do great works, banishing threats to the land like Sombra, purifying cursed lands, and finally...when my Sister did fall prey to the Nightmare, I wore all six together to use against...against her. And the spirit in the Elements had waited for that moment, and did nearly turn me into a slave of her will, to kill mine own Sister and then to make the Sun a tyrant destroyer of all ponydom had wrought."
"I did turn it's killing blade aside but a whit with all the love I could rally against it, and banished mine own sweet sister to the moon for a thousand years instead."
The clatter of a single chair falling the long span to the floor was all most noticed of Luna's sudden rise to her full height as she stood, wild-eyed and staring at her sister.
"I swore that never the Elements would be wielded by one, never again, and for a thousand years I held to that oath and more, for I gave the six pieces to the most true and good ponies I could find in the realm, for the time where they could be used without corrupting a single, foolish bearer to be it's puppet...and they saved my sister, and the realm in the time of Discord, healing and preserving all of Equestria with their deeds. You should bless them all, not curse their names! Curse....curse my own. I gave them the Elements when I could not bear them myself. I did not realize that the bonds of friendship would make them as one, so much so that the spirit within them would take ALL of them to cause such woe and pain. If I could...I would heal every mark, bless every troubled brow, make all the world right again for you, my little ponies. Please...please...forgive me for being such a fool. Take your anger and pull the feathers from my wings, the crown from my head, paint my mane with tar and hurl me into the rivers to drown. I will run, I will crawl, I will die to do what I can to make amends, and when you think I can do no more...do what you will."
"For the only bad pony here is me."
"And you are even worse a pony than you think, dearest aunt."
Celestia recoiled from the hate-filled voice as it whipped her ears and made her face duck close to the floor in shame. Blueblood rose to his hooves, the height of his seat putting his eyes on a level with Celestia's wide-eyed stare.
"I have an additional witness I would add to the list in light of the confession. Madam Speaker, will you allow it?", Blueblood almost crowed as the ponies around him began to inch away slowly, their sweaty flanks pressed as far into the walls of their alcoves as they could. One unicorn ducked down and shivered, only a green horn waving above her desk like a peeled twig.
"This- this is MOST irregular, Prince Blueblood!", Union Rose said in a fashion more suited to "The House is afire and about to collapse" than to "procedural irregularity".
"A Princess is interfering with the business of justice is irregular, Madam Speaker! I demand an additional witness to clarify the crime in light of this... of blatant pandering to the people!". The clopping of paperweights and the stomping of hooves began as a few clatters, but rapidly spread to bathe the room in thunderous agreement.
"HEAR, HEAR!" "Blueblood speaks for the ponies of Fillydelphia!" "WE DEMAND A FULL HEARING!" screeched the lone non-pony, a griffonesse from the Brooks Range Protectorate.
"Great flaming dragon doodles, where did this idiotic inbred hornhead find THAT to say at a time like this, to his own aunt?", Union Rose thought in a fit of disgust. "In light of these SMALL IRREGULARITIES, Prince Blueblood...one witness. Five minutes. No more. Call them, since you CLEARLY have decided to add someone I do NOT have on the witness list, in what I find to be a MOST irregular fashion."
Blueblood filled his lungs and let the contents roll out across the floor.
"I call to the podium, Princess Sunset Shimmer, consort to Prince Blueblood of the Seat of Canterlot, once-student to the esteemed Princess Celestia to give her statement regarding the criminal acts of the accused before us in the circle."
Celestia wobbled like a newborn filly as her knees gave out as her wayward, slightly battered but utterly self-assured and un-faithful student walked up to the small platform from which each witness had testified. A golden ring graced the base of her horn, and though it was clear that whatever journey had taken her to this place, she was more than ready to put it to good use.
"In addition to the horrible, horrible acts Celestia and her minions have done to the ponies of the Crystal Empire, she has had forbidden, dark magics by which she acts upon other races, hidden from good ponies behind a magical mirror she would allow none to understand save herself. I journeyed through this mirror when she forbade me and discovered the truth! Princess Celestia has hidden the mythical humans from ponykind. They are real! Any who would pass through the mirror would become like one, and they accepted me as one of their own, and by great acclaim made me their Princess, for the humans elect their Princess every year. For three years, I served in their magical lands as their crowned head, only to find a few days ago that magic, PONY magic, the magic of Celestia's Elements blasting through the portal to tear my kingdom from the earth and draw it to it's doom. Did you know how many innocent humans, MY humans you slew? Dozens? Hundreds? THOUSANDS! None could tell, for you gave them a grave between worlds where their poor, torn bodies will never know peace! Did you hate me so much that you killed them all to be rid of your "wayward student", the only pony Blueblood truly loved? It was a miracle that I escaped, that my darling Blueblood had sent his brave stallions to search for survivors in the Crystal Empire. It is DEAD, all of it DEAD! I have seen the dead pony walk, the howling ghosts in the broken buildings, and it IS YOUR FAULT!". With perfect timing, Shimmer's eyes watered with crocodile's tears. "You! YOU! YOOOOOOOU!" and with a third jab of her horn, she fell to the floor in a puddle of her own salty weeping. Blueblood leaped from his place and landed with a clatter of hoof-on-stone next to his wife, and gently led her from the chamber.
As Blueblood's aura pulled the door shut behind him and his "beloved", anarchy descended upon the rest. Ponies screamed at one another, pointed at Celestia, pointed at Luna, bucked the doors to their alcoves in anger until they clattered to the floor, shouted about criminal and innocent and bandied words even fouler than "horseapples!" and "darn!" that would have easily made a scandal on the politics page any other day. Today, no polite word spoke enough of how ponies felt. Union Rose broke her gavel hammering it in an effort to get order before resorting to flinging the broken thing away and bucking her hooves against the metal door of the Speaker's Stall. Sparks flew from her shoes and after a minute, the screech of bending brass and kicking legs quelled enough of the cacophony to let her yell above the lot:
"THERE WILL BE ORDER, BY THE SUN AND MOON, OR I SHALL BE FORCED TO CALL FOR PIES!"
And with that, the four guardponies opposite her produced discs of pastry topped with cream from beneath their wings and balanced them menacingly upon the tips. The threat of melee meringue finally reduced the politicians to silence.
"THE HOUSES SHALL CONSIDER THE WORDS OF THE ACCUSED AND ACCUSERS IN -PRIVATE- AND RETURN A VERDICT UPON THE DAWN OF THE SECOND DAY HENCE! LET THE CHAMBER BE CLEARED OF ANY WHO DOES NOT HOLD A SEAT AND THIS CHAMBER BE SEALED UNTIL SUCH TIME AS JUSTICE HAS BEEN SERVED!"
And with that, the two Princesses and their six friends found themselves herded down the marbled center to the stares and foam-flecked breathing of the rightful denizens of the legislature, past the fish-tailed equines of stone gamboling in their fountain, and onto two pegasus-drawn chariots. As they flew toward the castle, a crowd at the entrance to the Stables could be seen growing and beginning to boil...
---
...and in what was a seeming forever frozen eternal, a single crystal feather began to slip loose from Twilight's withered wings.