Twilight Sparkle had gotten some sleep. Starlight's morning coffee was now safely stored in Fluttershy's cottage - and considering the recent (fluttershy equivalent of) animosity between the yellow and the purple horses, it would be some time hopefully before Twilight was able to get her hooves on the stuff. Life in ponyville resumed to the normal calm, which could last anywhere between two weeks and a few months depending on random chance.
Pinkie Pie - with her uncanny perceptions to things going wrong, had practically a cult following at this point, her every 'sense' could trigger widespread emergency preparations in ponyville. One day, she had flappy ears, twitchy eyes, and a swishy tail, a combo she had not felt before. Suddenly, in the midst of lunch, she jumped on a table in Sugarcube corner, screamed that "THE CRYSTAL CASTLE IS GONNA FALL DOWN!" and rushed to Twilight's aid.
Starlight and Twilight were confused. Everything about the structure seemed fine at that moment, there were no problems that anypony could identify - top to bottom all seemed well.
Then, spike took the last bite.
Years earlier, Twilight had discovered her pet dragon had quite the affinity for munching on various fixtures and decorations that were in idle corners of the Castle. Evidently, the structure was quite delicious, but after a little bit of discipline she believed the problem had been satisfactorilly resolved. In the central room, Spike suddenly burst out of a painting, behind which was a long tunnel, from which a loud rumbling sound was emitting.
"I'm So SORRY!" Spike cried out. "EVERYPONY RUN!"
As it turned out, Spike had only curtailed his appetite for about a week before coming up with the ingenious plan to consume the structure from a series of tunnels swiss-cheesed into the very structure, using to his advantage that the dark tunnels could not be seen behind the translucent crystal walls, but he could see when a wall became too thin. Unfortunately, Spike was no structural engineer, and when he removed a column believed not to be essential, the miracle of finding the load bearer was a lesson pressed fresh on his mind.
Fluttershy rejoiced quietly to Twilight's misfortune, and then felt deeply ashamed for doing so. Applejack stared her down until she shrank to her knees. "But... but isn't it amazing... that such a little dragon could?" Applejack shook her head. Twilight muttered something about punishment and then wandered off toward Fluttershy's cottage. Starlight was busy trying to locate her personal belongings and didn't notice the Alicorn's dissapearance until too late.
Starlight teleported into the cottage but it was too late. Twilight was twenty three cups in and was completely Twily-nanas. Armed with her accessory ACTION-QUILL (TM) she was already furiously writing down a checklist of some kind.
Glimmer rushed to warn the others as the purple natural disaster flew in overhead at incredibly high speed. Landing on the castle rubble, she proudly declared. "Lets rebuild the castle!"
The mayor attempted to reassure the townsponies that this was a perfectly sensible idea for Twilight to have, despite the truly massive shipment of funding that was incoming from the Princess Celestia. Most of the town were eased, clinging onto the hope that the castle collapse was the disaster they had been waiting for over the past five weeks of unusual calm. The sight of the princess' frazzled mane however did not ease public opinion well enough. Roseluck packed all her things in a go-bag and pre-emptively moved into Octavia's house. The insurance had been working really well for her so far. Filthy rich was losing his shirt, she was sure.
More everfree forest was promptly clear-cut. When asked about the aggressive destruction of this natural treasure, Twilight dismissively waved her hoof and muttered something about progress. Applejack quickly wrote a letter to Celestia, and was most remarkably awarded the land and mineral rights to the 'distressed asset'. Fluttershy cried so hard she threw up. Applejack couldn't stop dancing back at home to her good fortune, she could cover the world with Apple trees at that rate, and she quickly formed an agreement with Rarity that would become the most mutually-profitable business conglomerate in Equestria's history. Rarity also was finally able to use that beautiful logo she designed.
Rarity and Twilight sat down then to design the new castle. Using nothing but imagination, frienship, and some back of back of napkin calculations, a new castle precisely in the same shape and form of the old castle was hastily constructed. It attained half its intended height before collapsing in a tidal-wave of timber, and a thunderous sound that heard as far away as Zecora's cottage. Twilight took notes.
"Well shucks." Applejack lamented, looking over the wreckage. "I guess I can spare some time from business plannin to help y'all design this - I designed the aero-train after all." She offered - two construction workers that overheard backed away slowly as Applejack grinned - chosing to remember the triumphs of the achievement instead of the failures. Applejack in truth was enjoying the engineering stuff, and had been providing Twilight with both XXX hard cider and coffee, often the two mixed. It wasn't quite as good as Starlight's coffee however.
Applejack traveled to Canterlot for inspiration. Despite making a complete arse of herself surrounded by fancy ponies as she went from building to building jumping on floors and looking at things - she came back to ponyville brimming with ideas.
"Stone!" She exclaimed, smacking her forehooves together.
"That's all you learned?" Starlight questioned.
"Yeah! Stone! Who'da thunk it. Are you second-in-engineering command?"
"No..." Starlight sighed. "No I'm not..."
The next castle would be constructed out of stone. Again in the form of the tree like the one before. A wooden structure was constructed as it was built for support, and every pony in equestria who was a mason, had some kind of gray blob for a cutie mark, or was named 'mason' was conscripted, along with a massive influx of cheap yak labor. Affordable housing was constructed near ponyville for the workers, half of which fell over in a stiff breeze. Slowly, Twilight was getting an idea.
With a keen, red-eyed obeservation of every detail while the castle was being constructed, Twilight observed how masonry construction worked. While the castle was collapsing into dust for a second time, suddenly, like a flash of lightning, it came to her that something could be built entirely of mortar and not stone at all! She began to experiment, while Ponyville recovered. Roselucks house was obliterated by a flying boulder.
The pie family became rich from the massive influx of rock orders to their farm, enough to purchase a tractor from the Flim-Flam Brothers Farm Implement Company. The tractor exploded. After a wrongful death lawsuit for a pet rock skyrocketed into a payment in the billions of bits when maud shed a single tear at the jury stand and everypony was so emotionally moved that the court had to adjourn to treat major depression in six out of ten jurors, the Pies had a settlement large enough to be able to abandon rock farming and live happily ever after.
Flim and Flam were so moved by Maud's tesimony that they came up with a marvelous idea to be able to pay it. The first Pyramid Scheme in Equestria was founded, the money was all given as per the settlement to the Pie Family. At the end of the massive Fiasco, Flim and Flam actually overpaid their lawsuit settlement, the pie family was saved from rock farming, and Maud found her pet rock a week later. Boulder had been hiding in a tree.
Back in Ponyville, Applejack and Twilight had invented concrete. Instead of trying to build another castle, they elected to build Roseluck's house out of the stuff. Strangely, Roseluck agreed, hoping for the best. A horribly square beige brick with windows and no door was constructed in the midst of Ponyville. It was knocked down, and rebuilt with a door. Twilight attempted to destroy it, and couldn't. Roseluck was overjoyed.
Rarity turned her nose up at the construction at first and then suddenly cried out "Ideaaaaa!" in a singsong voice. Archetectural brutalism was born. The crystal castle was re-imagined as a giant cube atop a thin stick, all made of concrete and absolutely covered with identical rectangular windows. Ponyvillians hated it. Twilight, faced with public outrage retreated to her castle to think.
After several nights of no sleep, she wrote to Celestia:
"Dear Princess Celestia. I believe some buildings in ponyvville are unsafe and I want to improve the lives of ponies. May I have permission to regulate what buildings are allowed in ponyville?"
Celestia didn't even read it. She replied with a form letter drafted by her legal team which not only gave Twilight this permission, but also the right to condemn buildings. Overnight, Twilight wrote 1127 pages of building codes. Ponyville was condemned. Applejack bribed Twilight with the stolen recipe to Starlight's coffee in exchange for an exemption for barns and farm concerns that specifically pertained to apples. The rest of ponyville was replaced with what looked like a nightmare of precast concrete buildings. Rarity loved it. Depression skyrocketed.
One week later, that disaster everypony had been waiting for happened and ponyville was destroyed again. Public outrage erupted as Twilight planned to rebuild everything except the mysteriously unharmed Brutalist Castle of Friendship or Something Like That. Everypony in town threatened to move out. Twilight relented.
"I suppose it all gets destroyed all the same." She resigned. Ponyvillians rejoiced and rebuilt. Inadvertently, while helping rebuild everything, Applejack invented the idea of prefabricated, modular housing. She crafted this idea with such brilliance that while ponyville looked the same from the outside, every home was built on a concrete foundation and was constructed of panels of standard size made in an assembly-line fashion. In some years, Suburban development would spiral out of control and Equestria would become a land of waste and misery because of this idea, but for the moment all was well.