[[quoteright:320:[[ComicBook/BlackPanther http://static.tvtropes.org/pmwiki/pub/images/Pantheropolis.jpeg]]]]
[[caption-width-right:320:[-In the dark heart of Africa lies the ShiningCity of Wakanda. …what? It's night time!-] ]]

The development and advancement of human civilization has been greatly spurred by tech sharing (or spying) between cultures and peoples as ideas are traded. While some have advanced socially, culturally and/or technologically faster than others thanks to internal stability and enlightened rulers, it's rare for a single society (much less city-state) to advance leaps and bounds ahead of its neighbors while keeping all its advances to itself.

Except in fiction, that is.

A common setting in {{pulp}} stories is the search or surreptitious discovery of an Advanced Ancient Acropolis. Hidden beneath the Earth in a LostWorld, an {{Atlantis}} under the sea, or concealed with advanced technology or magic, the Advanced Ancient Acropolis is the last city of an empire that reached space age [[BambooTechnology levels of technology]] and/or [[TheAgeOfMyth mythic magical powers]]. In some cases, [[LandOfOneCity it is an isolated city-state rather than one of an empire]]. Their claim to fame is that while the rest of the world was living in mud huts [[DecadeDissonance they had built a society]] of CrystalSpiresAndTogas and parked it in a [[strike:Medieval]] comfortable [[MedievalStasis Technological Stasis]]. All while [[HiddenElfVillage never revealing its existence]], though ancient legends of TheTimeOfMyths may speak of them.

Bonus trope points for avoiding all social decay while being completely insular, double bonus if they use CulturalPosturing on the "inferior" civilization the heroes hail from. One common variation has the Advanced Ancient Acropolis be in the same abandoned and ruined state as the one in Greece, having been destroyed, abandoned, [[UnderwaterCity sunken]], [[UndergroundCity buried]], wrecked from civil war, plague or some other [[EndOfAnAge misfortune]]. There might however [[LivingRelic be a last survivor]] in the form of a robot, golem, ghost, or immortal citizen. Sometimes this may expand to include the descendants of the original culture who have regressed into a simpler stage and scavenge in their ancestors' ruins. Heroes visiting these sites are advised that any [[LostTechnology ancient relics found]] are likely of the [[DurableDeathtrap dangerous]] {{curse}}d or LostSuperweapon varieties.

Of course, all of this can be explained if the founders of the city were [[SufficientlyAdvancedAlien aliens]] or from a HigherTechSpecies, or the survivors of a cataclysm that reduced the rest of the world to a lower level.

Common deconstructions frequently focus on just how [[TheHedonist decadent]] and out of repair such a society can become, which may in fact be [[SoiledCityOnAHill what leads to their ruin]]. Frequently, this is because their slave race of robots (or actual slaves) [[TurnedAgainstTheirMasters rebelled]].

See also SchizoTech and AdvancedAncientHumans. Compare CityOfGold and TempleOfDoom. A specific form of OlderIsBetter.


[[folder:{{Anime}} and {{Manga}}]]
* The demon world Pandaemonium in ''Manga/ChronoCrusade''[[note]]manga version only![[/note]] has technology leaps and bounds ahead of humanity. [[spoiler:Of course, this is because Pandaemonium is actually a giant living spaceship under the ocean and the demons are actually aliens.]]
* The ancient floating city in ''Laputa : Anime/CastleInTheSky''.
* The Mykene from ''Anime/MazingerZ'' and ''Anime/GreatMazinger'' inhabited the Greek island of Bardos in ancient times. Their technologic level was miles ahead of any other culture of the same time, and the rest of the world would need millennia to catch up. However, one earthquake shook their island and destroyed their cities, and they were forced to seek shelter underground. They founded another civilization BeneathTheEarth, but on the surface the only remainder left of their presence were abandoned, decaying ruins, and old legends about the HumongousMecha they used to defend their land.
* The Yamatai Kingdom from ''Anime/KotetsuJeeg'' is a "magic + technology" example.
* The abandoned [[{{Precursors}} Protoculture]] City in ''Anime/MacrossDoYouRememberLove'' In fact, there are Protoculture ruins all over the Milky Way in the ''Anime/{{Macross}}''-verse.
* Although we still know very few details, there was an ancient civilization in ''Manga/OnePiece'' destroyed by the World Government that seemingly created some of the most powerful weapons that history's ever known, each one capable of destroying the world.
* Nearly every temple pyramid that Esteban and his friends discover in ''Anime/TheMysteriousCitiesOfGold'' has some sort of solar-powered mechanism left behind by the ancient empire of Mu. One of them even serves as an aircraft hangar for the ''Golden Condor'', while another [[spoiler: is both a giant solar laser and the containment system for a fusion reactor.]]

[[folder:Comic Books]]
* Callahia, ComicBook/TheInhumans' city, and Atlantis in Creator/MarvelComics.
* The nation of Wakanda in Creator/MarvelComics.
* Atlantis in Creator/DetectiveComics and Comicbook/{{Aquaman}}.
* In ''Franchise/{{Superman}}'' story ''Comicbook/KryptoniteNevermore'' a mystical object called the Devil's Harp and other strange artifacts were discovered buried beneath an ancient, forgotten, unnamed city.
* Also Atlantis in ''ComicBook/BlakeAndMortimer'''s "The Secret of Atlantis".
* Paradise Island, pre-ComicBook/{{Crisis|on Infinite Earths}} home of Franchise/WonderWoman and the Amazons, had healing rays, invisible aircraft, and telepathic videophones. Themyscira, the ComicBook/PostCrisis version, wasn't quite so advanced originally, though it did "avoid all social decay"; later writers and {{retcon}}s would restore much of the "goofy" tech of the [[UsefulNotes/TheGoldenAgeOfComicBooks Golden]] and [[UsefulNotes/TheSilverAgeOfComicBooks Silver]] Ages.
* Gorilla City in Franchise/TheDCU may be portrayed as one

[[folder:Films -- Animated]]
* ''Disney/AtlantisTheLostEmpire''. Although by the time Milo and the crew gets there, [[LostTechnology the natives have forgotten how everything works.]]

[[folder:Films -- Live-Action]]
* ''Film/IndianaJonesAndTheKingdomOfTheCrystalSkull''. In Frank Darabont's unused draft, the technology was even more advanced than what was seen in the film.
* Some of the surprisingly-advanced BambooTechnology beyond modern inventions and {{durable death Trap}}s in ''{{Congo}}''.
* In ''Film/PlanetOfTheApes2001'', the Holy City of Calima turns out to be both ancient and advanced since its actually a starship from Earth that crashed centuries before.

* The Noldor domains in Beleriand and Númenor of the Dûnedain in Creator/JRRTolkien's Literature/TheSilmarillion
* ''Franchise/ConanTheBarbarian'' was chock full of these.
* In the ''Literature/RealmOfTheElderlings'' series, there's Kelsingra and several other ruined ancient Elderling cities found on the banks of the Rain Wild River and only accessible by using a liveship or taking the long, Skill-wrought road leading there from the Mountain Kingdom. [[spoiler:Due to their proximity to and co-habitation with dragons the Elderlings were able to take advantage of the latter's magic and develop what amounts to {{Magitek}}, yet their cities were destroyed in a cataclysm so devastating it changed even the course of the coastline.]]
* Creator/HPLovecraft[='=]s ''Literature/AtTheMountainsOfMadness'' features an example of this, notably of the alien civilisation subtrope.
* In Shane Johnson's novel Ice, two stranded astronauts find an advanced moon base built by humans from before Noah's flood. The technology is far beyond anything they've seen.
* ''Literature/{{Dinotopia}}'' has the lost civilization of Poseidos, which in its heyday had [[NinjaPirateZombieRobot robot dinosaurs]], remote control drones, computers, and all sorts of other SchizoTech.
* In Creator/AndreNorton's ''Literature/IceCrown'', the promise of Forerunner ruins motivates the mission to Clio, even though they are forbidden to make contact with the natives and have to do a lot to avoid it.
* In Creator/AndreNorton's ''Literature/{{Catseye|1961}}'', Ruhkarv was left behind by Forerunners. The one attempt to dig there led to disaster.
* H. Rider Haggard's ''Literature/{{She}}'' has the ancient city of Kor in Africa. The 1935 adaptation was in Antarctica and the 1965 movie went back to Africa.
* An OlderThanRadio example occurs in [[Creator/KurdLasswitz Kurd Laßwitz]]' short story ''Apoikis'' (1882). Here the narrator by chance comes to a uncharted island in the South Atlantic which is home to an advanced Greek city-state called Apoikis, which was founded by philosophers who emigrated from Greece after the execution of Socrates. Because they did not go through the Dark Ages and other reverses in the march of civilization, the Apoikians overtook European civilization in fields that interested them, particularly philosophy and the mind (most people who come to their island will be made to forget) and also beyond ancient Greek society (there are no slaves and an Apoikian woman is horrified to hear that in Germany girls are not taught ethics and logic in school). They dispose of futuristic technology, such as submarines and an impenetrable force-field, but are perfectly content to live among themselves and away from the barbarians of the outside world most of the time.
* ''Rogue Moon'' by Creator/AlgisBudrys centers around a mysterious (and deadly) labyrinth left behind on the moon by long-absent aliens.
* ''Literature/TheWitchlands'' have the city of Lovats, which has several features that leave its current occupants scratching their heads. Most notably, the city sits on top of several giant rivers and a waterfall, and the only way to access it is a set of enormous, indestructible bridges. It also has a sewer system that's possibly bigger than Lovats itself and may host an entire UndergroundCity of its own.

[[folder:Live Action Television]]
* Played straight and then subverted in ''Series/StargateSG1''. Our heroes discover references to the lost city of Atlantis and set out to find it. They think they've found it buried under the ice in Antarctica, but eventually they figure out that Atlantis is in another galaxy -- setting the stage for the spin-off series ''Series/StargateAtlantis''.
* ''Series/WonderWoman'': Paradise Island is an uncharted island within the devil's triangle. At 1942, The amazons wear togas and use arcs and arrows, but they had an invisible plane, a truth serum, and guns to use in her “Bullets and bracelets” challenge.
* The ''Series/BabylonFive'' setting in general, including its SpinOff ''Series/{{Crusade}}'', is littered with the ruins of civilizations that died out millennia ago, so much so that the MegaCorp Interplanetary Expeditions can turn sizable profits from mining them for LostTechnology. They're often plot points, too: Sheridan's wife was killed ([[spoiler:not really; she was capture by the Shadows and brainwashed]]) investigating Z'ha'dum.

* ''Pinball/{{Congo}}'' has Zinj, the hidden city filled with {{Killer Gorilla}}s.

[[folder:Tabletop Games]]
* Two sorts appear on Mars in ''TabletopGame/RocketAge''. There are ruined cities, still with some technology working, and the modern cities that endure to this day. The modern cities often still have access to advanced technology, but barely understand it or use it well.

[[folder:Video Games]]
* {{Atlantis}}, of course, in ''VideoGame/IndianaJonesAndTheFateOfAtlantis'', the [[AdventureGame cinematic game]] formerly known as [[FanNickname Indy 4]], with {{half human hybrid}}s and [[BambooTechnology Bronze Age]] {{Orichalcum}}-powered LostTechnology.
* Shevat, its rival Solaris, and Zeboim Civ in ''VideoGame/{{Xenogears}}'', though the former two were mostly just hoarding tech from the super-advanced starship that brought Humans to their world in the first place.
* Played straight with {{Atlantis}} in ''VideoGame/TheJourneymanProject 3''. While [[CityOfGold El Dorado]] and [[TheShangriLa Shangri-La]] were somewhat advanced in comparison to neighbors, Atlantis was a self-contained city-state that enslaved the crew of any ship that discovered their location.
* ''VideoGame/GoldenSun'' uses Lemuria, which was formerly the most advanced civilization in Weyard. After the powers of Alchemy were sealed by the lighthouses, the island closed itself off in an attempt to keep the remaining alchemy to themselves. Lemuria makes for an interesting case because, like the traditional Elf village setting, the citizens live for a very long time, and many of them deny that any decay has taken place at all. The king, however, shows the player's party maps of the world prior to the sealing of Alchemy and after, and there's a visible level of decay on a continental scale. This actually serves as a major turning point for the game.
* The ''Franchise/FinalFantasy'' series likes this trope:
** ''VideoGame/FinalFantasyI'': The flying fortress in the original NES version was obviously high-tech and patrolled by the Warmech, a robotic BossInMooksClothing. Later versions gave it a more medieval look.
** ''VideoGame/FinalFantasyIV'': The CrystalSpiresAndTogas Lunarian city.
** ''VideoGame/FinalFantasyV'': The Ronka Ruins were highly advanced, considering that upon activation they began to fly with the [[FridgeLogic Crystal of Earth]] and had teleporters and anti-air cannons installed. They also created the airship maintenance base Catapult.
** ''VideoGame/FinalFantasyVIII'': The Centra Ruins, though there's only one structure left from the ancient magitech culture. The existence of this civilization is {{justified}} by the setting; every so often for the past 10,000 years, a swarm of monsters falls from the moon, and this event (dubbed the Lunar Cry) has enough destructive power to destroy entire civilizations. Whatever technological disparity exists between empires is solely because the ones that go the longest without being hit by the Lunar Cry are also the ones that have the most time to develop.
** ''VideoGame/FinalFantasyX'': All ''over'' the place. The two main examples are huge subversions of the usual trope.
*** Bevelle is a living city that abandoned its LostTechnology for religious reasons. [[spoiler:Except that they didn't.]]
*** Zanarkand is [[spoiler:the summoned dream of an ancient, lost technological civilization created to preserve its people in the face of a war of extinction.]]
** ''VideoGame/FinalFantasyXII'': A {{downplayed}} variation; the world of Ivalice was certainly once in the throes of a major industrial revolution, and almost all technology in the setting is of modern innovation, but the ancient ruins in the game have teleporters. No one in the party really knows how they work nor cares for that matter. [[LampshadeHanging It's just something they expect ancient ruins to have]].
*** Ivalice games that are set after ''FF 12'' probably have that game to thank for their examples. The Clockwork City of Goug is a Moogle city in ''VideoGame/FinalFantasyTacticsA2'' in which old technology is excavated, and new technology is created. Long in the future in ''VideoGame/FinalFantasyTactics'', it's also a city where ancient machine relics are dug up and examined.
* {{Atlantis}}, again in ''VideoGame/EccoTheDolphin'', where the Atlanteans invented a time machine and escaped into the past when their city was destroyed. The machine remained until Ecco destroyed it after defeating the Vortex.
* Any place where Titan structures remain intact in ''VideoGame/WorldOfWarcraft'' is this by default. Most are concentrated on areas of land close to the north and south poles. [[OurDwarvesAreAllTheSame The dwarves]] have taken particular interest in these old Titan leftovers after relatively recent discoveries of a connection between their race and some of the old Titan constructed races, and make it a point to try and find and excavate such sites.
* There are several signs of the advanced Echidna civilization on Angel Island in the ''Franchise/SonicTheHedgehog'' games, but the most technologically advanced is the Sky Sanctuary which is in the clouds and has teleporters.
* Columbia in ''VideoGame/BioShockInfinite'' is a single city that is apparently advanced enough to wage war against the rest of the world. It stole most of its inventions through Tears in reality that allowed them to see possible futures. [[spoiler:This is how they gained Vigors; by stealing them from [[VideoGame/BioShock1 Rapture]]]]
* Inverted with the city of Shinto in ''VideoGame/AsurasWrath'' as well as the rest of the Shinkoku Trastrium civilization. All the buildings and sculptures fits the look of Ancient Hindu and buddhist buildings and sculptures that would seem far too advanced for their time, but in a twist, the story takes place several thousands, if not millions of years in the future that merely is made to look like an ancient civilization.
** The DLC ending reveals that the game in fact took place 870 million years in the past!
* In ''Franchise/TheElderScrolls'', most prominently seen in ''[[VideoGame/TheElderScrollsIIIMorrowind Morrowind]]'' and ''[[VideoGame/TheElderScrollsVSkyrim Skyrim]]'', the former cities of the [[OurDwarvesAreDifferent Dwemer]] are this along with being [[UndergroundCity Underground Cities]]. Since the Dwemer [[RiddleForTheAges mysteriously disappeared]] thousands of years ago, their cities have fallen to ruins. However, the Dwemer were extremely technologically advanced, with their creations unmatched by any other group in the thousands of years since. They were masters of combining enchantment-based {{Magitek}} with SteamPunk machinery, and were known to [[RealityWarper bend the laws of nature and physics]] to [[RagnarokProofing make their creations last]]. It is all now LostTechnology, and their ruins still have {{Eternal Engine}}s running and MechaMooks on patrol. Their citadels around Red Mountain in Vvardenfell, the former epicenter of Dwemer culture, and Blackreach, the former Dwemer capital of Skyrim, are especially massive and advanced.
* The isolated citadels of the ancient Jotuns in ''VideoGame/GuildWars2'' can be considered this. Located high in the mountains, they were created by the highly-advanced Jotun culture before their civilization tore itself apart.
* Many 4X- and Grand Strategy Games may make the player (or at least in theory other AI players) advance way beyond their neighbors, more so than realistically possible.
** In the ''VideoGame/{{Civilization}}'' series, one civilization can be building a star ship to the next system while others are still fighting with axes and haven't even discovered the wheel.
* ''VideoGame/{{Bioforge}}'': The Phyxx base, the last relic of this advanced alien civilization, found on a distant moon.
* In ''[[VideoGame/WorldsOfUltimaTheSavageEmpire The Savage Empire]]'', the Kotl civilization is a {{Mayincatec}} civilization with advanced technology.
* The Xel'Naga temples in ''VideoGame/StarCraft''
* The FloatingContinent of ''VideoGame/{{Ys}}'' in the second game of the series, the Ancient City in ''Ys IV'', the lost kingdom of Kefin in ''Ys V'', and the ruined city of Kishgal in ''Ys VI''.
* In ''VideoGame/TalesOfPhantasia'', the ancient city of Odin was more or less on par technologically with Earth in 1994, and even looked like a modern metropolis. It suffered a major universe-appropriate WMD-style cataclysm and ended up buried, but reasonably intact. Contrast with the mostly medieval style of everything else in the world.
* In ''VideoGame/TalesOfVesperia'', the ancient [[OurElvesAreBetter Kritya]] society invented the Blastia, but were wiped out by an apocalypse. The player even visits a Krityan ruin early on the where they find some of the only golems in the game.
* ''VideoGame/TearsToTiara2'': Tartetos, an entire city floating in the middle of a lake. Complete with walls light enough to float, but stronger than anything humans can build. The grounds keeper is a [[OurDragonsAreDifferent Dragon Goddess that looks like a young girl]].
* ''VideoGame/ChronoTrigger'': The Kingdom of Zeal includes floating cities and other advanced technologies, and is more advanced than any civilizations that would follow for thousands of years.
* In ''VideoGame/{{Phoenotopia}}'', humanity on Earth recovered after the ancient war, and ancient Earth is seen as one of these.
* Justified in ''VideoGame/PhantasyStarIV''. Any ancient civilization dug up and studied in Motovia were built and controlled in ''VideoGame/PhantasyStarII'' by the hyperly advanced alien AI called "Mother Brain", which had been designed to provide convinient and somewhat lazy life for humans [[spoiler: as the villain's gradual poison apple plan to dominate the planet.]] When Mother Brain was killed by the heroes at the end of the game, Motavia's global system mulfunctioned, and the planet's civillization was reverted into DesertPunk society like it used to be.
* ''VideoGame/{{Uncharted}}'' makes the lost civilizations Shambala (Shangri-La) and Ubar (Iram of the Pillars) the objectives of the second and third installments. The first game involves El Dorado (the legendary lost CityOfGold) but reinterprets the legend (turning it from a lost city to a [[spoiler:golden idol]]).

[[folder:Web Comics]]
* In ''Webcomic/DubiousCompany'', Walter comes from a MagiTek nation that resembles a mix of modern day and CrystalSpiresAndTogas and may or may not be FluffyCloudHeaven. The rest of the world follows more closely to a StandardFantasySetting and Walter has to piece together most of his tech from scratch.
* The titular lost city in ''Webcomic/{{Fweeeeetopia}}'' is a floating-city-type, staying in the air through massive engines.

[[folder:Western Animation]]
* More than eight hundred years AfterTheEnd the New York City subway serves as the home of the [[EldritchAbomination Lich King]] in ''WesternAnimation/AdventureTime''.
* In ''WesternAnimation/ThunderCats2011'', BigBad SorcerousOverlord Mumm-Ra's FuturisticPyramid is the long-abandoned variation, with Mumm-Ra as its single LivingRelic inhabitant until he begins marshalling his forces. Much more capacious than it first appears, it's inferred as the source of all his army's OffscreenVillainDarkMatter. [[spoiler:This is due its origins as a [[TheBattlestar battlestar]] so massive and populated it housed enough people to invade a planet.]]

[[folder:Real Life]]
* [[http://en.wikipedia.org/wiki/Garamantes The Berbers]] had a civilization in the Hellenistic era (it fell a little after Rome did) that even managed to irrigate the Sahara—well enough to grow ''dates''.
* The deserts of Saudi Arabia and the Sahara contain lost cities that are only now being discovered. One city in the deep desert, [[http://en.wikipedia.org/wiki/Iram_of_the_Pillars Iram of the Pillars]] was assumed to be just a fanciful myth but was in fact a major metropolis with [[AluminumChristmasTrees multi-story high-rises]] completely buried in sand. Another in Yemen is still inhabited.
* Just about every continent contains lost civilizations we know little about because the remains got scattered. Most of ancient Persian architecture and civilization is lost, for instance.
* The Mound Builders around the Mississipi River had elaborate agriculture and trade networks, in support of a chiefdom system probably somewhat similar to feudalism. They fed a population of tens or even hundreds of thousands, despite only using copper for ornaments—they did all that with stone tools (and no wagons). The Mound Builders were so advanced 19th century Anglo-Americans assumed their earthworks must've been the work of AncientAstronauts or {{Atlantis}}, because they didn't believe any Native Americans were capable of that level of engineering.
* The Olmec, best known for their colossal sculptures, probably laid the foundations for all later Mesoamerican civilizations, having innovated the "ball game", civic design, mathematical concepts and agricultural techniques, and probably also a great deal of cosmology (they originated ritual bloodletting, for example, although we have no evidence they actually practiced human sacrifice—that's their successor, the "Epi-Olmec". No one's sure why the Olmec declined, although we can assume they abandoned their urban sites because their decline, whatever caused it, meant they no longer had the resources to maintain cities.
* The Classic Maya, and to a lesser extent the early Postclassic (most famously the Postclassic center Chichen Itzá), had an extremely complex urban civilization and the only decipherable written language in the New World.
* Teotihuacan, whose name (in the Aztec language Nahuatl) is the very dramatic "Place of the birth of the gods", is a giant abandoned metropolis. Even more significantly its Maya name means "Place of Reeds", which is the homeland of the Aztecs' ancestors, the Toltecs ("Reed-people"). Only, we're pretty sure the people who built Teotihuacan weren't anyone related to the Toltecs, but either the Totonacs (who claim they built it, and the Aztecs agree with them), or, as all the archaeological and linguistic evidence indicates, a Mixe-Zoquean group; more confusingly ''everyone'' seems to have been represented in the city, it had distinct ethnic neighborhoods, so it's very difficult to pin down as "a city of the X people".
* Rome's civic works were extremely advanced, the kind of thing only a massive central bureaucracy and the backs of millions of slaves can accomplish without modern industrial infrastructure. We've found steam-powered toys and even an ancient computer in Roman ruins, several of which had much better sewers than Victorian London. For centuries after Rome's fall, its works (which, again, had "empire" resources to play with) were seen as the pinnacle of engineering—even by cultures that had surpassed Rome in raw technical ability, like the medieval French, whose arches were stronger, whose wooden houses had stone chimneys (there was a reason Rome had all those fires), and whose industry used the first mechanized factories ever, powered by water-wheels attached to camshafts (invented in about the 10th century).
** It's not just that, they even have a [[LostTechnology forgotten recipe]] for "Roman Concrete". This stuff's harder than modern portland versions. It's why the [[RagnarokProofing Roman]] cities are still safe to walk around in; and while the Egyptian Pyramids and the Great Wall of China also exist, the Colosseum still has an entire city to keep it company.
** Some of the city of Rome's ancient infrastructure, such as their roads, the water and water waste systems are still used today, at least in part - at least two of the ancient paved roads are still in use and open to the public, the Trevi fountain is '''still''' supplied by the ''Aqua Virgo'' aqueduct, and not insignificant parts of the modern Roman sewers were in fact built at least 1800 years ago.
* The [[http://en.wikipedia.org/wiki/Indus_Valley_Civilization Indus Valley Civilization]] cities had planned layouts and a sophisticate sewage system 2000 years before the foundation of Rome. The city of Mohenjo-daro is thought to have housed 35,000 inhabitants at its peak.
** Mohenjo-daro actually had a better sewage system than some MODERN Indian cities. And, to make it even more impressive, some of the fringe-theorists believe the reason it got abandoned is because it got NUKED. Don't ask how, it's a long story.
* The Angkor civilization of modern day's Indochina was all but forgotten in the centuries following its demise until in 1861 the Frenchman Henri Mouhot stumbled across its ruins deep in the jungles of Cambodia. Later research indicated that the city of Angkor might have boasted a population of more than one million people, more than any other in the world before the Industrial Revolution.