Suppose for the moment that one is a science fiction or fantasy author, and further suppose that one wanted to posit a past great civilization whose existence comes as a complete surprise to modern folk. Let us also suppose that one wanted overlooking this lost civilization to be plausible… How might one go about this?
I’d tend to reject the “a secretive cabal always knew but kept it secret” explanation. People gossip. People love to show off their insider knowledge. People sometimes accidentally cut and paste entire sections of texts they’d really rather the world not know about into their tweets. Even valuable trade secrets tend to leak out given enough time. So where to hide a lost civilization? Here are five possibilities, to be used together or in concert.
Catastrophic social collapse is an obvious possibility. Not something picayune like the fall of the Western Roman Empire. That didn’t even manage to erase Latin. Something more like the Bronze Age collapse might do. That appears to have wiped whole languages off the map, which is handy if you don’t want the newcomers who move into the vacated region to read the informative inscriptions on any ruins the previous order left behind.
In pre-industrial days, you could do quite a lot of damage to a civilization with a bit of well-timed climate change or (if the iron theory about the Bronze Age collapse is right), counterproductive technological progress. This is probably still true. A hypothetical civilization ten thousand years in our future might not know about us if our grand finale included catastrophic climate change and a global thermonuclear war.
(See, for example works like Poul Anderson’s The Winter of the World, in which one of the few things known about the world culture of the distant past is that its decline coincided with the sudden appearance of a surprising number of large craters in the middle of what had been cities.)
Of course, thanks to all their stonework, even the Bronze Age collapse couldn’t hide that there had been grand civilizations in the region, even if it made it hard to find out just who they were. Ditto the stuff one might dig up around those nuclear craters.
There’s a catch. We notice that the Bronze Age cultures existed because they used familiar technology. Even if you don’t know who created a ruined temple, the ruin proclaims that someone built it. If, however, our vanished civilization used tools unfamiliar to us, or used familiar technology in unfamiliar ways, we might not necessarily recognize the evidence of human technology for what it was.
In fantasy, this sort of thing often involves magic, which moderns lacking magic would not recognize. SF authors have the option of handing their lost civilizations technologies that are entirely unfamiliar to us. A real-world example might be terra preta, which was not interpreted as evidence of indigenous soil management until recently. For that matter, Europeans pouring into lands whose indigenous populations had been annihilated by Eurasian diseases seem not to have noticed the degree to which Pre-Columbian cultures managed what the Europeans took to be wilderness.
Geology offers another useful tool for erasing civilizations, although it may require careful selection of location for one’s lost civilization. If, for example, some great pre-anatomically-modern-human culture happened by bad luck to build their elegant palaces on the slopes of the no-doubt impressive volcano that once occupied the site of Lake Toba, those grand edifices would now be scattered in very small fragments across a surprisingly vast expanse of Southeast Asia.
On a similar note, humans are fond of seashores. The majority of our great cities are within 100 m of sea level. Sea level is subject to dramatic changes. If, for example, the unfortunate Mount Toba culture mentioned above also populated the low-lying parts of Sundaland, their ruins would now be well under water. It’s easy to overlook drowned cities.
Still, many relics of civilization—mines, stone buildings, depleted resources, the odd patch of radioactive fallout—are durable over long time spans. The solution here is tip one’s hat to The Silurian Hypothesis: Would it be possible to detect an industrial civilization in the geological record? and turn to deep time. If you don’t limit yourself to human terrestrial civilization, then you have access to geological processes unlike any humans have been unfortunate enough to live through. Quite a lot of the Earth’s surface has been reprocessed or erased: you could park your ancients on top of what became the Siberian Traps or in the middle of what is now the Great Unconformity to erase virtually any evidence they existed.
There’s also deep space: plant your hypotheticals on ancient Venus, for example, and not only has the place been utterly transformed over the last billion years, but we’ve accomplished only the most rudimentary exploration so far. Extrasolar worlds are unknown to us to an even greater degree.
Perhaps the most powerful tool for concealing an ancient civilization in plain sight is simple bigotry. It does not matter how compelling the physical evidence is if the people interpreting it are blinkered by blind prejudice. It did not in any way advance the cause of correctly understanding terra preta for what it was that the scientists of the time did not believe the Amazon had ever been home to an indigenous civilization. Correctly interpreting the ruins of Great Zimbabwe was enormously complicated by the fact that doing so was philosophically and politically inconvenient to the people in charge of the studies.
No doubt you have your own favourite methods of hiding lost civilizations. Feel free to mention them in comments.
In the words of Wikipedia editor TexasAndroid, prolific book reviewer and perennial Darwin Award nominee James Davis Nicoll is of “questionable notability.” His work has appeared in Publishers Weekly and Romantic Times as well as on his own websites, James Nicoll Reviews and Young People Read Old SFF (where he is assisted by editor Karen Lofstrom and web person Adrienne L. Travis). He is currently a finalist for the 2020 Best Fan Writer Hugo Award and is surprisingly flammable.