"The architecture is... is..." Rarity's muzzle scrunched as the ghostly unicorn struggled for the words to say.
"Lemme guess..." Pinkie Pie smiled sideways as she and the rest glided after their anchor. "'Fabulous?'"
"I'm trying to give an assessment of its construction," Rarity said. "But... I'm at a loss for words..."
"Is it like anything you've ever sensed before, Rarity?" Twilight Sparkle asked.
Rarity slowly shook her head. "This material is strong. Sturdy. I would almost say unbreakable."
"Yeah, but there are lots of cracked and broken bits!" Pinkie Pie said, pointing down at the multiple debris-strewn platforms. "Just look at all the glass!"
"Well, of course, Pinkie. But..." Rarity shuddered. "What I'm trying to say is that it's nothing at all like any of the structures I've witnessed since Rainbow Dash woke me back in the Nealand Atoll." She gazed at the tall spires and their glossy surfaces. "Whoever constructed this was exceptionally mastered. This material is very, very old... and yet it's withstood the test of time quite masterfully, if you ask me."
"In other words..." Twilight Sparkle's eyes narrowed. "...it wasn't built by anything dwelling on the Dark Side."
Rarity sighed. "I cannot for the life of me see how."
"Then what does that mean?" Fluttershy asked as they all floated alongside Rainbow Dash. "None of the ponies stuck here had a hoof in it? Not the Dark Vigil? Not the Emeraldinians? Not the changelings under Tchern's command?"
"Really?!" Pinkie Pie cackled. "Do you really honestly think a bunch of gooey bug ponies vomited this all up?!?"
"What about alicorns?" Applejack suggested. "Celestia's kind are purdy darn good at raisin' barns." She shuddered. "Big... harmonic... immortal barns..."
"I can't imagine how or why alicorns would have built this," Twilight said, gesturing at the endless rows of buildings and skyscrapers and interconnecting platforms. "For one, it's just too vast and... opulent for the likes of alicorns. No... this was meant for ponies to live in. A huge population of ponies."
"So?" Pinkie shrugged. "Maybe they just built it for ponies!"
"But Pinkie—you're forgetting!" Twilight exclaimed. "The alicorns could only light one side of the plane! They chose the side that Equestria eventually blossomed in. This half—this entire Dark Side—they had to abandon to darkness and chaos! The only exception is the Midnight Armory! They built that, but even then they didn't have enough numbers to stay there and guard the Harmonic Prism from the outside! They just had to trust that the magics inside the structure were sufficient enough to ward off evil elements. Also... if the alicorns somehow did build an ancient city over here, don't you think Whitemane would have told Rainbow Dash? Or Mortuana? Or Celestia and Luna for that matter?"
"It could have been a secret," Rarity suggested.
"Naw..." Applejack shook her head. "The alicorns ain't the lyin' type."
"Plus..." Fluttershy looked at Rarity. "...what would be the purpose of this place? Why even keep it secret?"
"Well, darling, is anything living here?"
Fluttershy sighed, eventually shaking her head. "Aside from random patches of wildlife, this place is completely devoid of any equine population whatsoever."
"You sure you ain't sensin' a chaotic absence of life?" Applejack suggested.
"No." Fluttershy stared at her. "I'm not."
Applejack bit her lip.
"Nothing's been here in ages," Rainbow Dash finally said. Her eyes traced the landscape below. "And I do mean ages." Her nostrils flared. "Not ponies. Not changelings. Not trolls..." She turned and looked behind her—towards Edgeside. She caught sight of Flynn and Kepler emerging from the mountain cave with the glowing, chaos-driven wagon. "...this place has been long forgotten. Somehow... I wouldn't be surprised if even the alicorns have no recollection of it."
"Then..." Rarity blinked thoughtfully. "...Rainbow Dash, you're suggesting that this place may be older than the alicorns' presence on this plane."
Rainbow bit her lip.
"Is that what you're suggesting, darling?"
Rainbow opened her muzzle to answer—but then nearly bumped into a feathered figure. "Guh!"
"Aaaaaaaaackies—Oh, it's just Wildcard." Pinkie Pie exhaled, smiling tiredly. "Seriously! Somepony should put a bell on him!"
"Jordan..." Rainbow Dash recovered her breath, hovering in place before the Desperado. "Found anything?"
He nodded, then gestured: "Look. Different building."
Rainbow raised an eyebrow. Wildcard flew sideways, and the petite pegasus joined him. Soon they were both levitating above the lopsided dome that had crashed into the broken skyscraper.
"See!" Pinkie Pie pointed. "It's totally not indestructable!"
"My goodness!" Rarity held a pair of hooves to her dainty muzzle. "Now that's alarming!"
Applejack looked aside. "You mean you didn't sense this before?"
"How c-could I?" Rarity gulped. "Both the skyscraper and this errant structure are built out of the same material!"
Rainbow glanced at Rarity upon hearing that.
"But... they look so very different," Fluttershy stated. "The building looks like metal and the dome looks like marble..."
"Look at those columns," Twilight Sparkle said, tapping her chin in thought. "The aesthetic..."
"Oh, most assuredly, darling." Rarity smiled. "It looks antique. Almost Pre-Celestial. Why—don't you remember the Hearth's Warming plays? Ha! If I didn't know better, I'd say the architecture was positively Pegasopolitan."
Rainbow's lips pursed. Her ears perked up. "... ... ...Stratopolitan."
Her friends looked at her.
"Rainbow...?" Twilight exhaled.
Rainbow Dash took a deep breath. "I've seen this sort of architecture before."
Wildcard cocked his head to the side.
Rainbow Dash flew closer to the lopsided dome. She approached the upper circumference, where multiple etchings of winged equines were frozen forever in mid-flight. The mare ran her blue hoof along the feathery motifs.
"This... this is a building that belongs to Stratopolis... a Sentinel..."
"A Senti—what?" Pinkie Pie remarked.
Applejack squinted. "Are ya talkin' about that crazy floatin' sky city that you and yer Jury friends fought your way through?"
"Twilight..." Rainbow glanced aside. "...do you remember when I told you about Stratopolis?"
"Of course I do. It sounded absolutely frightening."
"Chrysalis had taken it over," Rainbow said. "It was her place of operation... her nursery for hatching her changeling army, hidden in a neverending snow flurry." Her brow furrowed as she stared at the engravings up close. "But it didn't always belong to her. Stratopolis was ancient—as old as the plane and maybe even older. The ancient pegasi controlled it, and at some point... they unleashed something horribad. It killed them all off and it nearly killed us."
Fluttershy stepped in. "Didn't it cross paths with Commander Hurricane?"
"Yes." Rainbow nodded. "It did. And Hurricane—who was almost the Austraeoh herself—gave her life along with a bunch of brave Pegasopolitans to move the dang thing out of Equestrian airspace. A few of Hurricane's soldiers survived, and they crash-landed a piece of Stratopolis in Alafreo to the east. That's how Durandana came to be."
"But..." Pinkie Pie's brow furrowed. "...where does this 'Sentinel' thing come in to play?"
"That's what Queen Chrysalis called Stratopolis," Rainbow Dash explained. "Razzar as well." She flew backwards, gazing at the dome at large. "From what I eventually learned, they were satellite structures—a floating collection of buildings that could go anywhere and monitor the various pieces of Urohringr."
"Some protection!" Pinkie Pie cackled. "Looks like the ancient pegasi messed up big time!"
"Well, that much is obvious, Pinkie," Applejack said. "Ain't they responsible for the Sunderin'?"
Rainbow Dash didn't respond to that. She was too busy staring—mesmerized—at the out-of-place structure. "Did... did Stratopolis fly by here?" She rubbed her head in thought. "But... how? When? It... it had to have been so very long ago..."
"Seems a bit of a stretch," Fluttershy said.
Rainbow flashed her a look. "Huh?"
"You're thinking that Stratopolis flew here?" Fluttershy remarked. "And yet somehow ended up floating about at random along the Light Side?"
"Fluttershy's onto something," Twilight Sparkle declared. "The solution has to be a lot simpler, Rainbow Dash."
Rainbow Dash fell silent. Pondering.
"There's..." Pinkie's eyes crossed. "...more than one Sentinel?"
Twilight Sparkle nodded. "It would make sense. Something as big as Urohringr? To be properly monitored, the structure would need multiple satellite structures."
"Do ya remember ever hearin' about more than one of 'em, Sugarcube?" Applejack asked.
"Now that you mention it, I kinda do..." Rainbow shuddered. "But... that's just mind-blowin'." She gulped, looking at the dome with a paler expression. "Another Stratopolis? Floating around and causing more havoc?"
"Maybe it's not as dire a situation as the one you encountered Chrysalis' forces in," Twilight suggested.
"I don't know, Twi..." Rainbow fought shivers. "...the ancient pegasi messed up in a lot of ways. The Sundering is just the tip of the iceberg. You don't wanna know what was inside that thing."
Twilight gulped. "I think you told me plenty."
Silence.
Rainbow Dash's ears drooped. She looked aside and noticed Wildcard gawking at her. "Oh... uh..." She smiled nervously. "Hey, Jordan. Sorry, I... uh..." A sigh. "... ... ...you listen to any of that?"
He nodded. A hand-sign: "Everything."
"Uh huh." She winced. "Any thoughts?"
The Desperado swiftly gestured something Rainbow didn't yet understand.
"Huh?" she squinted.
Pinkie Pie murmured, "I think he's taking a metaphoric poopie."
Applejack cleared her throat. "She ain't wrong."
Before Rainbow Dash could comment—
"Pssst!" Ariel hissed from a distance. "Rainbow Dash! Double-yoo! Over here! I've got something to show you!"
Rainbow exchanged glances with Wildcard.
The Desperado nodded. He flew off in a swift glide and Rainbow followed shortly behind.
"This should be good," Rainbow muttered, giving the broken buildings behind her one last forlorn look.