Lost Cities is a My Little Pony: Friendship Is Magic fanfic written by Cold in Gardez. Its most notable feature is its narrative style, which features no dialogue, action or characters. Instead, each chapter consists of the description of the ruins of an abandoned city, with the narrative being revealed to the reader as they're gradually shown more information hinting at the city's history, culture and demise.
The story consists of seven chapters, each focused on a different city. The four original ones describe the capitals of the unicorns, pegasi and earth ponies before the unified into Equestria, alongside Luna and Celestia's original capital. Two more were later added describing the original pony city that was abandoned during the events of "Hearth's Warming Eve" and a submarine seapony city; the seventh and final chapter describes a city from another fan work.
A sequel of sorts exists, Natural Histories, which describes the lives of living creatures that made their homes among the broken ruins of the lost cities. Another work by the same author, The World is Filled with Monsters, shares the same setting; notably, due to being set long before the show's time, it depicts a few of the ruined cities of the original work during a period where they were still inhabited.
Several works by other authors exist that were inspired by this story's narrative style, although they're not directly connected to it. These include The Seal of Wax and Glass, The Gentle People, Unknown Architecture, Keskiyönnon, Far Kobresia, Aletheia, The City that Breathes and The Land of Glass and Stone.
This work contains examples of:
- Citadel City: Derecho, the Fortress City of the Clouds, was a floating fortress as much as it was a city, girded by a wall a thousand feet high and built primarily to keep watch over Equestria's northern borders.
- Domed Hometown: The seapony capital was an unusual example — rather than a straightforward dome, the royal palace of their queen was an immense structure built out of eggshell-thin, transparent mother-of-pearl, large enough to fill a large section of the Starlight Trench and to house entire cities under its vaulted ceilings.
- Eldritch Location: The Everfree's description leans towards this more than it "simply" being The Lost Woods. It stands in defiance of the magical laws that govern the rest of the world, and every year tries to creep a little farther out and swallow a little more land. Its depths are filled with increasingly alien and dangerous life — parasitic, chimeric or magically reactive plants and powerful predators are already common on its borders, and things grow more dangerous further in — and it's crossed by paths that somehow ward off the predators, but which periodically vanish from existence in a manner that, according to magical monitoring, causes them to occasionally just... never have existed at all.
- Epigraph: Each chapter begins with a quote from Invisible Cities by Italo Calvino, another work about fantastical cities, in some way relevant to the themes of the city described within it.
- Floating Continent: The pegasus city of Derecho was built of clouds, which were packed and condensed into a mountain-sized, floating mass on which the city itself was built.
- Grim Up North: North of Equestria are cold lands, empty save for an ancient, abandoned pegasus city. Beyond that are cold, barren mountains, home to the griffon tribes. Beyond that nobody lives, and there is only a vast cold wilderness of snowy forests haunted by ghosts and spirits, and then a vast glacier at the top of the world, holding the ruins of the first city in its depths.
- Human Sacrifice: In the end of the first chapter, it's implied that the unicorns of the Heartspire had take up the habit of sacrificing earth pony captives in an altar at the top of their tower.
- Look on My Works, Ye Mighty, and Despair!: A central theme of the story is the downfallen glory of ancient empires. Time and again, rising civilizations built vast monuments, raised immense cities, and filled them with art and wealth and symbols of their great and lasting power. Nothing remains of their glories, now, beyond lonely ruins home only to the wind.
- Mage Tower: The Heartspire was a unicorn-built and ruled tower miles in height, and so large that an entire city was built inside it with quite a bit of room to spare. However, it wasn't the good kind of wizards who lived there...
- The Magocracy: The Heartspire was a tower-city ruled by powerful unicorn wizards, who reveled in their immense power and mastery over nature and disdained ponies incapable of spellcasting.
- Mobile City: After its abandonment, the cloud city of Derecho began to drift passively on the winds, slowly migrating through Equestria's skies.
- Our Spirits Are Different: The great boreal forest in the north is haunted by ghosts and spirits. Most are indistinct things, little more than floating lights bobbing among the trees or a half-seen glow in the sockets of empty skulls, but others are vast and powerful, like a great winged shape whose wheeling form covers the sky from one horizon to the other.
- Planimal: The bizarre plants of the Everfree Forest include spiderbrambles, bushes whose fruit are living, fully formed spiders capable of spinning webs and catching insects.
- Recursive Fanfiction:
- The last chapter, "The Waters of Mynnkyun's Harbor", describes the ruins of a city whose end is depicted in another story, The Last Dreams of Pony Island.
- The story itself has inspired a number of Spiritual Successors, each describing the ruin and decay of a grand, magical city in some forgotten corner of the show's world.
- Soiled City on a Hill: Although the Heartspire is implied to have started out with good intentions, it eventually became a corrupt, tyrannical society that embraced slave labor and equine sacrifice, which caused Celestia and Luna to destroy it.
- Taken for Granite: After most of Lith's inhabitants left the city, those that remained behind gradually turned to stone; in time, the city became home to nothing but half-buried statues.
- Underwater City: The seaponies of the Endless Ocean lived in a city built at the bottom of the Starlight Trench, and housed within a great palace spun from nacre. It's also mentioned that Aquastria, another submarine seapony city, still exists under the Eternal Ocean on the other side of the continent.
- Unperson: After the seapony emperor's reign ended, his subjects toppled his statues, destroyed or defaced most of them, and chiseled out and erased every mention of his name that could be found.
- Urban Ruins: Each chapter describes the abandoned ruins of a fantastical city long after its abandonment and destruction. The writing mostly focuses on themes of decaying grandeur and of the downfall of hubris, as the halls, monuments and achievements of what was once a mighty city sit lonely and abandoned, slowly succumbing to the ravages of nature.
- Will-o'-the-Wisp: The spirits of the northern forest include little motes of light that flit among the trees, wavering and bobbing, vanishing and reappearing, fading and waxing, tempting travelers to wander deeper and deeper into the wood to get just another glimpse of their fascinating dance...
- Always a Bigger Fish: This is a major theme in "The Fountain", where no matter how dangerous and aggressive something is there always something else that can destroy it — unseen monsters preying on the cockatrices and timberwolves, a colony of giant spiders that overwhelm and consume a mass of voracious, magical slime mold, and in the end a simple salamander egg, whose fiery hatching incinerates everything else in the glade.
- Cargo Cult: The nymph-ponies in "The Quarry" form one of sorts, revering the metallic debris left at the bottom of the flooded quarry where they live as holy gifts from the spirits due to their inability to manufacture steel themselves.
- Chekhov's Gun: The salamander egg in "The Fountain", laid at the start of the chapter and not mentioned again until it hatches at the end, incinerating all the other creatures in the clearing.
- Extreme Omnivore: Salamanders feed on anything organic — fresh plants, eggs, animals too injured, weak or stupid to avoid them, carrion, rotting leaves, and anything else they stumble across; it's all fuel to them.
- Festering Fungus: A small patch of slime mold in "The Fountain", growing on a magic-soaked rowan log, becomes tainted and twisted by sorcery and soon grows into a vast, hungry tide of yellow slime, creeping over and consuming entire groves of trees as it spreads mindlessly through the forest.
- Fiery Salamander: Salamanders are reptilian creatures native to the Everfree Forest. They smolder constantly with fire, scorching the ground they walk on and burning paths through vegetation through simple contact. They lay eggs like lumps of carbon, which feed on the energy of dying things until they have enough to hatch in a fiery, extremely destructive explosion.
- Killed Offscreen: In "The Fountain", a disagreement between the leader of the cockatrice flock and a younger specimen sees the youngster ousted and chased away. After he vanishes into the thick veneration, there's a loud crash, the sound of breaking branches, and an abruptly cut off bird's cry as he runs afoul of one of the Everfree's many predators.
- Magic Eater: The oaks that grew over the ruins of Everfree learned to consume the magic that permeated the ruins of the old Equestrian capital, absorbing it and making themselves strong. It allowed them to overwhelm the other trees of the forest but also changed them, turning them dark and twisted and causing the forest to become the wild, haunted and terrible Everfree Forest of canon.
- Nothing Is Scarier: At one point in "The Fountain", something terrible and powerful approaches the timberwolf pack. It is never seen, remaining hidden by the undergrowth, and is only described as a large shadow, a stench of death and magic, and a presence that intimidates the wolves, before, still unseen, it retreats.
- Spontaneous Generation: This is proposed as a possible reason for why fish are present in the lake formed from a large quarry, despite it having no inlets or outlets that fish could have used to reach it and having been filled only by rainwater; it's mentioned that sometimes mice will just appear in stacks of hay, or maggots in meat, and that something similar may have happened here. A more mundane explanation is that fish eggs were carried in on the feet of birds.
- Unwitting Instigator of Doom: In "The Quarry", one of the nymph-ponies dives down to the bottom of the lake to retrieve some metal, as has been done countless times before. Unknown to him, the large piece that he finds and pries free is the locking mechanism for one of the sluices originally intended to drain the quarry the lake formed in; by opening it, he drains the entire lake out into the sea, causing his own demise and dooming his society.