The least fantastic version of this is an exaggerated version of how nomadic societies work in real life. A large group of people moves around, carrying tents, large carts or other shelters either in disassembled form or by hauling them around on wheels, and sets up a temporary city when it decides to stop moving. When the group sets off once more, the city is disassembled and carried off until a new spot is chosen. Most fictional examples, however, go further than this — rather than being moved around piecemeal, a city moves as a single, solid block. This typically takes the form of a large platform, with the city on top, given motile power by huge wheels or caterpillar treads. Some examples give the city mechanical legs, sometimes turning it outright into a colossal, animal- or human-shaped Humongous Mecha so big that a respectable community can live in its insides.
Most examples of this take place on land, but moving cities can inhabit other environments as well. Some exist on the sea, ranging from nomadic fleets to masses of ships lashed to each other to solitary vessels the size of cities to giant floating platforms with cities on them. Aerial examples also exist, held up by giant rotors, balloons or good old-fashioned magic or Technobabble and roaming the skies of their worlds; see also Floating Continent. Mobile cities may occasionally have minds/AI of their own too. City-sized spacecraft or space stations, while they technically fall under the definition of this trope, don't usually qualify since, unlike other examples, they are not confined to the surface of a planet.
The chief issue with such cities is that making a large settlement ambulatory requires a lot of complex infrastructure and some way to keep everything powered, whereas a regular static city just needs someone to build enough houses in the same general area. Consequently, mobile cities tend to be built for very specific reasons. Often, it may be that staying put just isn't an option — perhaps the city consumes too many resources to depend on a single area, or perhaps something, such as climate extremes or enemies, makes staying in one place dangerous. A particularly common science fiction variant involves planets where the day, the night or both cannot be lived through, and the locals need to constantly follow the day-night terminator; for these examples in particular, see Mercurial Base. Alternatively, however, this may be nothing more or less than a cultural tradition or affectation.
Another side effect of these cities is that they make it very difficult for nations to exist, at least in the traditional sense. Keeping tracks of borders and of whose land is whose can get pretty difficult when every population center can just wander to the other end of the continent should it decide to. As such, mobile city-heavy worlds will either exist under an all-encompassing world government or will have each city be its own self-governing unit, with few hard ties to others. Formal alliances and unions of cities can still exist, but will often be groupings of allied nomad settlements with few or no territorial claims.
This may overlap with Layered Metropolis, in which case expect Urban Segregation to take place on such cities, with the lowest levels dedicated to maintenance workers and engineers tasked with keeping the cities operational (akin to crewmen shoveling coal in boilers on steam-powered ships back in the early 20th Century). The third-class commoners will generally be stuck living in this noisy and polluted environment. The middle levels will usually be the general civilian area with lots of standard middle-class homes, while the uppermost levels are reserved purely for the rich first-class nobles and politicians who call the shots, complete with extravagant manors and castles to boot.
For less extreme cousins of this trope, see Base on Wheels and Moving Buildings. Supertrope to Mercurial Base. Compare Turtle Island. And for this trope taken Up to Eleven, check out Planet Spaceship.
Not to be confused with the city of Mobile, Alabama.
- Chrome Shelled Regios: Humanity lives on mobile cities called "Regios" after an apocalyptic event wrecks the world. They serve as protection against the polluted atmosphere and the giant man-eating Filth Monsters that roam the planet, and the cities frequently engage in competitions against each other for resources.
- DARLING in the FRANXX: The setting takes place on a mobile fort city called a "Plantation", and there are several others like it roaming the Earth. Their sole purpose is to protect the remainder of humanity from a race of aliens called the Klaxxosaurs, whom they fight off using Humongous Mecha.
- Deca-Dence: The titular object is a giant mobile city that humanity lives in. It's actually run by a Mega-Corp that uses it as a hub for their cyborg employees to play an MMO game with Artificial Human avatars that they control remotely.
- Gargantia on the Verdurous Planet takes place mostly on a far-future Earth covered by an endless ocean, whose natives now live on Gargantia, a great city-fleet roaming the world ocean.
- Girls und Panzer has moving ships that are big enough to house a small town district.
- One Piece:
- Discussed with Iceburg, the mayor of the island city-state Water 7. Thinking of the increasingly intense "Aqua Laguna" storms that periodically ravage the island, he considers turning Water 7 into a huge mobile island vessel.
- Germa Kingdom's "territory" consists of several big ships that can combine into one and separate when necessary.
- Overman King Gainer features a city on wheels, functioning as a base and living space for both the heroes and the entire population of the city that was mobilized. The enemies have control of the railroads, so quick transit of their forces makes a mobile base necessary for the Exodus.
- Robot Carnival: In the first and last shorts we see the eponymous Carnival, an abandoned robot city that was once a massive traveling circus. Its automated movement on massive treads and malfunctioning equipment have turned it from entertainment to terror, as it towers several hundred feet in the air and is bigger than the towns it flattens as it unknowingly continues its preprogrammed circuit across a blasted landscape.
- Soul Eater: In the anime, Death City is revealed to have legs and to be able to get up and walk around. This is set up early, with Dr Stein pointing out that the only way for Death to chase the Big Bad would be if Death City grew legs and started walking, lampshading the ludicrousness of such a thought and making it so that no-one would assume that it could, in fact, happen.
- Castle in the Sky: Laputa is a fortified town able to fly in the sky, but which has been abandoned by its former inhabitants.
- Magic: The Gathering: On Ikoria, some humans live in the makeshift flying city of Skysail, made up of hundreds of baloons and dirigibles which can break apart into individual balloon fleets and scatter in the event of an aerial monster attack. Its main survival strategy is mobility — besides staying far above most of the world's monsters, Skysail is constantly moving around and never stays in one sport for long, in order to stay out of the flying monsters' migration routes and to avoid making itself a target for aerial predators.
- Dungeon Keeper Ami: Ami's Iceberg Dungeon, which is a ship made to move Ami and her forces from one continent to another. It's basically holding an army, but it's also self-sufficient, being able to farm all its food.
- Lost Cities: After its abandonment, the cloud city of Derecho began to drift passively on the winds, slowly migrating through Equestria's skies.
- Romance and the Fate of Equestria: The Bazaar, which serves as the centerpiece for a fairly large portion of the story, is a floating city that travels the world, returning to Equestria every few years.
- John Carter: In the Disney adaptation, Zodanga is reinvented as a mobile city dragging itself across the surface of Barsoom by dozens of giant shovels strip-mining the planet as it goes.
- After the Revolution: The City of Wheels, more commonly known as "Rolling F*ck," is a fairly realistic example. Being a nomadic anarcho-socialist commune largely consisting of a convoy of cars and RVs with hydroponics on the roofs, and a three-story tall mining rig that looks like a spider made out of scaffolding.
- Calamity: Idilithia is an interesting variant on this trope. Buildings on one side of the city are constantly crumbling to dust, but the other side expands and grows new buildings at the same rate. So, instead of moving like a car or train, it moves like a spot of mold moving across a piece of bread.
- Cities in Flight: The "spindizzy" — the Applied Phlebotinum that allows for Anti-Gravity, Force Fields, Artificial Gravity, and Faster-Than-Light Travel — works better with larger masses. As a result, eventually, entire Terran cities cut themselves free of the planet and soar out to the stars as independent, nomadic city-states.
- In The Inverted World, the City is laboriously dragged forward on rails through the distorted landscape outside to keep up with the translat optimum. People's ages are even measured in miles...
- Mortal Engines: The series focuses on the mobile "traction cities" that sprung up following an apocalyptic nuclear war, which rove endlessly over the plains of Eurasia on giant caterpillar treads and consume each other for the resources they need to keep themselves running. Traditional, static cities still exist, and those who live in mobile cities think of people living in them as barbaric and backward. After all, it's only natural for cities to move across the landscape eating smaller cities and towns to survive.
- The cities are typically built on stacked circular tiers, narrowing towards their tops, and social rank and wealth tend to determine where you live — the rich and powerful tend to be on the top, while poorer people get the lowest decks and the full brunt of the smoke, grime and noise from the cities' engines.
- Mobile cities in other parts of the world use different methods of travel than the usual wheels or treads, such as cities that slide across the polar ice caps on giant bladed runners, others that float on the oceans and even one that's airborne.
- The issues and implications of such things are also given focus — northern Eurasia is reduced to a field of churned mud and gnawed-on mountains by the constantly moving, resource-hungry cities, and the fact that this system is all predators and no prey also makes it unstable, as it has no actual input of energy or material, and ultimately doomed. Even at the start of the series, the traction cities are growing very low on resources and desperate for "food".
- Propeller Island, a novel by Jules Verne, takes place chiefly on Standard Island, an artificially-built moving island home to millions of people. It's also split by a bitter feud between its starboard and larboard inhabitant, which threatens the city's enduring survival.
- The Scar: The pirate city of Armada is made out of thousands upon thousands of ships lashed together and repurposed into buildings, and moves nomadically on the oceans on the world to avoid detection. In its case, its mobility comes from the Avanc, a mind-bogglingly titanic sea monster that was harnessed to the city and now pulls it around.
- In The State of the Art, a short story collection by Iain Banks, the opening tale "The Road of Skulls" features a pair of pilgrims trying to reach a city. The city is actually on huge wheels and is perpetually moving away from them, laying the road they're traveling on.
- The Stormlight Archive: Played with but ultimately subverted. The location of the city of Urithiru was lost long ago by the peoples of Roshar, but maps existing at the time of the Knights Radiant depicted it as being located immediately next to that mapmaker's nation's capital city. Jasnah and Shallan theorize that Urithiru was a city which moved from place to place, but ultimately it's revealed to exist in the mountains and be accessible to these capitals through portals.
- Wind on Fire has the rival cities Ombaraka and Omchaka. These are driven by sails, and whenever they cross paths they attack each other by launching smaller "land-sailers" at each other like torpedoes. Most of these intercept and destroy each other; actually scoring a hit on the other city is quite rare.
- Power Rangers Lost Galaxy: The main setting is Terra Venture, a giant mobile space station that contains a literal domed city.
- Cyberpunk v3.0: Road Cities came around after biker gangs became extremely popular, with campers and caravans eventually being traded for this trope. The faction in-game is known as the Rolling State.
- Dungeons & Dragons:
- DragonMech: The Moon is, for unknown reasons, heading closer and closer to the world, breaking up in nightly meteor showers that devastate the surface of the planet. This has wiped out most surface civilizations, and the survivors have either retreated underground or within gigantic steam-powered Magitek mecha with armor sturdy enough to withstand the meteors and the ability to move around to avoid the worst conditions and the monsters brought to earth by the lunar rains. These are large enough to carry entire cities on their backs, and often host unique ecologies in their interiors in the bargain. Most City Mechs are self-governing units, but the five dwarven mechs are united in the Stenian Confederacy and are the single most powerful political force in the world.
- Planescape: The Crawling City in Gehenna, the closest thing to a capital city for the fiendish yugoloths, moves upon thousands and thousands of demonic, fireproof legs capable of fording rivers of lava and moving vertically up cliffs, and can move between any of the plane's layers. The city's ruler, the General of Gehenna, uses its mobility to keep his location hidden from enemies both within and without the yugoloth race.
- Exalted: The city-ship of Denzik is built out of hundreds of large junks lashed together for stability, each bearing a marketplace on its upper deck and with lower decks filled with living quarters, storehouses, shrines and amenities for those living there, forming a true floating city. Denzik follows an endless, looping route along Creation's great western ocean and the inland sea around the Blessed Isle, trading with each port it meets along the way to purchase exotic cargo to trade at further stops and the agricultural output of entire countrysides to provision itself for its endless journey.
- Nihliesh very likely was this in the distant past — it's a gigantic, many-legged vehicle the size of a city, with a good-sized settlement built on its back. It ceased functioning long ago, however, and was already immobile and half-buried when its current inhabitants found it centuries ago.
- The city of Joira is built on, in and beneath the carapace of the granthu, a titanic crustacean that lives deep beneath the sea. The creature itself migrates along an endless circuit of the abyss, periodically coming close to shore before heading back into the deep, and the Joirans have adapted to this perambulatory nature and periodically trade with other underwater cities as Joira passes them by.
- The Scuttling City is an octopus settlement off the coast of the Lands of the Dawn. It consists of a large number of spheres constantly shifting in position respect to each other, and which have mechanical tentacles on their undersides. The city is always in motion, using the tentacles of whichever spheres currently happen to be low enough to move across the sea floor.
- The town of Umdera is periodically disassembled and hauled to a new location where it is rebuilt. The longest the elders recall the village ever staying in one place is ten years and the briefest just a few months.
- Several living cities crawl, float, or fly across the landscape of the Liminal Shore. The Windborne City of Nera is a flying example and always on the move, stretching across the sky in a vast train visible from a few hundred miles away on the surface. It follows a migratory path that sees it encircle the entire globe of the Liminal Shore every thirty to fifty days, generally speaking.
- Warhammer 40,000: The roleplaying games include two examples:
- Ambulon, the wandering city, is built on the back of a titanic legged machine that walks across the unstable rocky centre of Scintilla's main continent. The machine itself predates the Imperium's arrival to Scintilla — Ambulon was built on it secondarily. The city itself is a mobile settlement, making endless tours of the planet's oil, gas and gemstone deposits to harvest resources to send to its other, static cities. As with all other complex technology in the setting, Ambulon's mobility is poorly understood and kept going mostly by ritual — no one knows exactly what would happen should it stop, and nobody wants to. As a result of these factors, the engineer guild that operates its engines and navigation wields immense political power. The city itself also experiences considerable Urban Segregation, driven by a need for stable housing against the sway of the city's movements — the powerful live in its center, the poor and the workers in more precarious spots along its edges, and the most disenfranchised and outcast have to cling to its underbelly and risk being scraped off when the city passes over a hill or ridge.
- The planet Zayth has been left scarred, barren and borderline unlivable by millennia of warfare, strip-mining to feed the wars, and the ceaseless movements of the cities themselves. Its people are now reduced to living in hive-ships, tracked megalopoli carrying ridiculous amounts of (occasionally starship-scaled) weaponry, used to battle other hive-ships for Zayh's dwindling resources.
- Warhammer: Age of Sigmar: The Idoneth city of Galanaur rests on the back of a colossal sea monster called a Great Scaphodon, which slowly moves across the seafloor and takes the city with it. Galanaur was originally built in the Realm of Ghyran, but the Scaphodon's movements have long since caused it to move into Ghur.
- 80 Days: The city of Agra is essentially the Taj Mahal and its surrounding environs on several massive Steampunk legs periodically walking throughout India. It's even mentioned that the political status of the city is being contested, as the Brits claim that it's part of The Raj while the rest of the peninsula claims that, since Agra sometimes wanders into their territory, it can't be a British holding. In-game, it actually counts as a mode of transportation on one particular route. On the top, you have the gardens and the majesty of the Taj Mahal. Below decks, you have the steaming and clanging underbelly where thousands of multicultural workers live and work, ensuring the safe operation of the walking city (naturally, lots of big levers and valves).
- Arknights: "Nomadic cities" in-universe are this writ large, as major urban areas are now semi-mobile and move around given areas so as to avoid local capital-C Catastrophes when they strike; living in one place for too long has become rather dangerous and risk-prone, as the immobilized Chernobog demonstrates in chapter one. It's also not made extremely obvious at first, but the Rhodes Island company's base is a (somewhat smaller) instance of these and is the very Rhodes Island from which the company takes its name. You get a brief look at it at the start of chapter two, and it features in update trailers occasionally.
- BioShock Infinite: The game takes place in Columbia, a flying city made out of numerous platforms held aloft by a fleet of giant blimps, balloons, reactors, propellers, and "quantum levitation". It's fully mobile and capable of intercontinental travel, and after its launch was sent off across the world as a display of American power and skill. Relations between the country and the city turned sour when Columbia revealed that it was heavily armed and capable of serving as a roving weapon of mass destruction when it brutally put down the Boxer Rebellion, which led Columbia to secede from the US and vanish into the clouds.
- Breath of Fire II: The entire city of Township gains the ability to fly after an optional quest. This is required for the best possible ending.
- Civilization: Beyond Earth: The Rising Tide DLC introduces aquatic cities. These cities are able to slowly move to an unoccupied adjacent hex after a certain project is completed. This is also how they claim territory (unlike land cities, which use culture). The North Sea Alliance specializes in these kinds of cities.
- Endless Legend: The Roving Clans build their cities on the backs of massive Setseke beetles the size of a city block. Under most circumstances, the beetle hibernates as the Roving Clans peddle their wares and build, but in times of change the citizens can awaken the beast ("Setseke, ho!") and set off. While in motion, the city generates food, influence, Dust and science, but cannot build anything. The beetles are surprisingly agile for their sheer size, having the same four movement points as most infantry units.
- Halo: The Covenant capital city of High Charity is an chunk of the Prophets' old homeworld that was pulled into orbit and turned into a mobile space station. Relying on an ancient Forerunner ship for mobility and power, it is capable of traveling all over the galaxy while housing thousands to millions of Covenant citizens and troops.
- Punishing: Gray Raven:
- The "eternal train" Oseram consists of several building-sized carriages. It runs through Eurasia in order to power the filters that protects its population from the Punishing virus and uses its mobility to position itself as a Merchant City that can buy and sell anything from anyone.
- Later, the story introduces the Nona Ouroboros Night Vessel, a ship that's been turned into a massive floating city. It has similar mercantile leanings, but it's quickly overshadowed by the numerous hidden agendas being pursued by rulers of the vessel. It also is ultimately subordinate to Kowloon, a stationary city-state in the middle of the ocean.
- World of Warcraft: The city of the mage order known as Kirin Tor, Dalaran, was rebuilt some time after the Third War and turned into a sky base of sorts for the heroes of Azeroth, twice. It was moved from the shores of Lake Lordamere to Crystalsong Forest in Northrend the first time, in order to spearhead the crusade against the Lich King during the expansion Wrath of the Lich King. It was then moved to the Broken Isles to spearhead the crusade against the Burning Legion in the Legion expansion.
- Orion's Arm: Mobile cities, while not extremely common, exist on multiple worlds. Some are simply elaborate art projects or lifestyle whims by the setting's hypertech civilizations, while others exist as responses to specific needs.
- In general, a number of types of these cities exist. Some walk around on large legs — these are favored when earthquakes are an issue — while others are platforms on top of large, moving mats of nanotechnology. Some people instead inhabit very large, humanoid or animal-shaped robots, built to house anything from villas to cities in their insides or on their backs; these are explicitly treated as flashy, ludicrous indulgences made to satisfy someone's artistic whim rather than serve a practical purpose. Most of these settlements, regardless of type, are also provided with advanced AI and are often fully sapient.
- The Gigerant Traveling City is an especially exotic example, as it doesn't move in the traditional sense — rather, its citizens are constantly demolishing its trailing edge and building at its leading edge, causing the city to slowly crawl over the surface of its world. Each new district is slightly to drastically different from the ones it replaces, keeping the city constantly changing and novel. It also houses a large organization devoted to restoring natural environments in its wake, as its movement plays merry hell with the ecologies of the areas it passes through.
- The twin planets Laurel and Hardy are close enough to exert very strong tidal forces upon each other, and as a result both are rocked by frequent and very strong earthquakes, tsunamis and volcanism. The locals adapted to this by building all their settlements on legs. The people of Hardy favor cities supported by multiple legs, which can absorb tectonic shocks, rise above tidal waves and just go somewhere else if an area gets covered in lava. Those on Hardy instead prefer giant, habitable mega-mechs, which pace endlessly around the world's circular ocean and respond to the worst shocks (and strong winds) by sitting on specialized, chair-like tending stations.
- My Little Pony: Friendship Is Magic: While this isn't given central focus, Cloudsdale — a flying city made out of clouds — moves around through the skies of Equestria, managing the weather and changing the seasons as it goes. A few episodes' stories are set into motion by Cloudsdale's circuit taking it over Ponyville — it passes by in "Hurricane Fluttershy" to pick up a load of water for making rain and in "Tanks for the Memories" to get winter started.
- Talespin: Panda-La can rise off the ground using giant balloons and fly through the air. This was done to suit its inhabitants' taste for conquest — when the pandas decided they wanted to take over a new land, they moved their city to their target location, subjugated it, and landed there until they set their eyes somewhere else.
- While very few have ever actually been realized, several proposals have been made for creating permanent marine settlements — most, at least in part, as a way to get out of paying taxes. While most simply consist of building static artificial islands, others envision adapting methods and technologies used by cruise ships to build immense, fully mobile vessels capable of hosting permanent communities.
- The most elborate such proposal, termed Freedom Ship, would essentially consist of an 1,800-meter-long condominium built on a series of linked barges, containing its own hospital, school, and commercial and office spaces, all pulled by a giant motor unit and making an endless circuit of the world's oceans, periodically stopping at ports for supplies and shore leave.
- ResidenSea, officially called MS The World, was actually built, mostly because of its much more modest aims. It's essentially a cruise ship built to work like a condominium, contains a grocery store and assorted amenities, and can house up to 200 permanent residents and 280 crewmembers.
- Aircraft carriers are like military bases roaming the sea. A Nimitz-class carrier is 300+ meters long with a crew of 6000+, carrying all amenities necessary to keep such a population healthy and running.