The 10,000 year skyscraper

Question

If someone wanted to construct a skyscraper (bigger being better) that would survive thousands of years without maintenance, what would they make it out of?

It can be built from any plausible current/cutting edge/semi-futuristic materials but should be something that you can actually picture people using for large scale construction so no platinum/iridium alloys ;) Concrete's probably out too as it would likely start showing problems after a few hundred years.

The idea being in the near(ish) future lots of new buildings are built from said materials (because they're tough/cheap/abundant/renewable/recyclable etc.) Sometime after, there is some kind of cataclysm (haven't worked out an appropriate one yet). Some 10,000 years into the future, a few of these great buildings remain (even just one or two would be ok), inspiring awe in whatever underdeveloped civilisation is still around at the time.

Answer 1

Build a Pyramid

The Pyramids are halfway to your desired 10,000 year life span already. They are a little worse for wear, but they are definitely still standing.

First, lets assess the criticism that the pyramids are not skyscrapers. The great pyramid at Giza (139m) was the tallest building in the world until the Lincoln Cathedral was completed in 1311. Then, after the Lincoln Cathedral burned down, and St. Mary's church in Stralsund was hit by lightning, the Great Pyramid was on top again until 1874 when St. Nikolai's was completed in Hamburg. Skyscrapers started off much smaller. The Home Insurance Building in Chicago, the first building supported by a fireproof metal frame was 42m in 1884. The 1895 American Surety Building in New York was 92m. The 1903 Flatiron building in New York went to 94m, and finally in 1908 the Singer tower went to 187m and beat the pyramids.

Even today, the pyramids would be tall for a modern American city. A 150m pyramid would be the 14th tallest building in Boston, 19th tallest in Dallas, 7th tallest in Denver or Minneapolis, etc.

Second, lets assess the claim that the pyramids are just a pile of rocks. The ancient pyramids did clearly have internal structures, although not very large. If you were purpose building a pyramid to house more, you could make more room on the inside. The internal volume is 88 million cubic feet, as opposed to 37 million for the Empire state building. So there is plenty of room to build things and have lots of rocks left over.

Finally, lets address the age of the pyramids. They have lasted 5000 years built with 5000 year old technology. That is significant. The builders did not have metal to work with, only the most rudimentary mathematics, etc. And yet look how long their creation lasted? Instead of using limestone, a modern pyramid could be made of granite. If the pyramid was continuously occupied, it wouldn't be vandalized (much of the current damage was done by vandals who stripped the outer casing). Metal struts could be added to support the interior and allow more usable space inside.

In conclusion, if you want a building to last a long time, make your building into a mountain.

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As is noted by Tim B. if you want your building (or anything) to last a long time, build it in the Egyptian desert with no winters.

Answer 2

Self-healing concrete.

It works by embedding tiny capsules in the concrete containing bacterial spores. When the capsules are broken by water penetrating the concrete, the bacteria are released and begin to metabolise - and one of their waste products is calcite (a component in limestone). The calcite seals the crack, good as new.

The technology is definitely in its infancy - it can currently only heal very small cracks, and once a capsule is used it's gone for good. Nearish-future technology could certainly expand the size of the cracks that can be fixed, and perhaps include a way for the capsules to be reused.

Secondly, while it's true that modern concrete tends to crumble within a couple of decades, that's not an immutable fact of what will always happen to concrete or concrete-like materials.

2,000 years ago, the engineers of the Roman empire discovered what they called opus caementicium, and what we today call concrete. Their mix included volcanic ash, and structures built with this material is still standing today. The Pantheon in Rome is the classic example, built around 100 AD, with a massive concrete dome. It's still standing and structurally sound.

Buildings and structures using Roman Concrete are still standing. Bridges, reservoirs, and aqueducts were built with this material, attesting to its versatility and durability

Combine advances in self-healing concrete with a breakthrough in affordable Roman-style concrete, and you could have a pretty impressive material. Combine that with some of the structural ideas in other answers, like pyramids, and structures surviving 10,000 years seems quite workable.

Answer 3

I don't think an inanimate building is an option either. I'm going to admit this may not be within the technological scope you want, it certainly wouldn't exactly look the way you want and there are some real issues about why this would be a desirable choice, but if you're willing to stretch, how about a genetically modified tree.

The current tallest redwood is about 380ft tall. Certainly not a mega skyscraper, but genetics, proper farming and a little imagination might get you to 500ft. They're big enough to live in, and trees are fairly resilient to having stuff carved out of them.

The oldest living bristlecone pines are thought to be 5000 years old. Maybe there are older trees? Maybe their not so huge stature is a barrier to longevity?

The widest tree is an 80ft in diameter redwood. That's bigger than an apartment; people could live in it.

On a more tree friendly world, one with a lot more CO₂, the tree could be much larger and hardier than is possible today.

Answer 4

Life After People did come up with an answer, but you are not going to like it.

Of all the human artifacts that were profiled on Life After People, the one which had the longest potential lifespan was the Apollo Lunar Landers. They will sit on the Moon, preserved in vacuum as recognizable artifacts for almost a quarter billion years. Deep space probes like Voyager and New Horizon speeding out into interstellar space might also last as long, before the effects of cosmic radiation, being pelted by high speed dust particles and other effects of the space environment erode them away.

So creating a structure on the Moon will certainly outlast anything built on a geologically active planet like Earth. Considering that any structure will need at least 5 meters of shielding to cover it, it is conceivable that it will survive eons before being eroded away, and might even still be recognizable as an artifact 5 billion years from now when the Sun engulfs it in its red giant phase.

Answer 5

Why build a structure when it's possible to hollow out an existing structure like a mountain?

There are over 200 underground structures in eastern Turkey. One of the best examples is Derinkuyu, a cave city that is estimated to have been able to accommodate a population of 20,000 people in 13 underground levels. The exact age of the underground cities are unknown but they have been found to contain artefacts from 800 BC. The cities were linked by underground tunnels that stretched for miles. There's a 5 mile long tunnel linking Derinkuyu with Kaymakli.

If you want to insist on building a structure that would last the test of time then you could build your skyscraper using today's technology. Afterwards clad the building using rock cut into interlocking irregular shapes as seen at the Sacsayhuaman UNESCO World Heritage site in Peru. The irregular pattern will help the structure withstand earthquakes.

Both structures were created almost 3,000 years ago, engineering feats that we would struggle to accomplish today using the tools which we know were available at the time. Peru and Turkey are both subject to regular seismic activity so we know the structures will last the test of time.

If Derinkuyu could accommodate 20,000 people it would more than meet the skyscraper requirement considering that the World Trade Centre complex accommodated 50,000 people before its destruction in 2001.

Answer 6

No, there is absolutely no way to build such durable (modern) structures. Absolutely nothing humanity has built in the modern age, or will build in the next centuries will still be around 10 thousand years from now.

Note: I'm talking about structures meant for habitation here, not nuclear waste storage sites, etc.

And disregarding any one material lasting that long (never mind keeping its shape and size), the complex system (that's what a building is - a system) as a whole would eventually decay.

Such structures would come under assault from a variety of forces, year after year. We're talking temperature changes, humidity, strong winds, earthquakes, etc.

It's sufficient for one bolt to come loose, one part to start vibrating, and eventually a whole mess of bolts and parts are slowly coming apart, with likely disastrous consequences.

Note: I can't find it right now, but there was a study commissioned by an american agency, to study how a nuclear waste site might be labelled as a dangerous area in a manner which will last for several thousand years (beyond memory of the United States as a nation). The best they could come up with is carving the warning in a stone tablet 50 foot tall, and sealing the whole thing in some sort of super hard resin. Even then, they had some doubts of it surviving due to seismic activity. So you can throw the idea of a building surviving several times that time span right out the window.

Answer 7

Depends on what your definition of skyscraper is. In the 1800s the definition was like 10-20 stories. Now, it's like 40-50.

The biggest problem is height with little support--the tallest structures on earth have sway and are built to move, basically because of high winds at a certain height.

Certain structural designs do stand the test of time--and those are pyramids. There's not as much that can go wrong over a millennia or more...

But the very design of a skyscraper is not tenable for the sort of time frame you are talking about. It doesn't matter what it's made out of. There are too many interdependent parts as well--and it would just take one thing to bring it all down.

But hey, let's give it a go. I want your skyscrapers to survive. So--sand. a big sand storm sweeps in, covering & filling your structure(s) and protecting them. Maybe they are covered for thousands and thousands of years, before another sandstorm partially reveals them, just in time for the heroes to see them. They might still be filled with sand, won't seem as tall, and definitely won't be structurally sound.

Make it like Dubai or something...I dunno. They have some crazy buildings. Although Dubai didn't fare too well in Life After People... Link to vid.

10,000 years is a long damn time, so take it down. Also, watch the entire Life After People series. It's an education. Most structures like what you're talking about go after a couple hundred years. Even if you had perfect materials I can't see you doing more than doubling that...

Answer 8

None of the materials we currently have can produce a skyscraper that can last 10k years without maintenance. Not even promising materials currently on the horizon can.

Good concrete without steel reinforcement can last for a long time, but it is heavy, stiff and brittle, 10k years will likely see more than a few major earthquakes that could crumble it.

Solid rock is also quite durable, but while a good option for building something like a pyramid, it is impossible to build a skyscraper out of it.

Compressed earth is quite durable too, especially with proper care, but even without it, there are some compressed earth structures dating back thousands of years. But again, not an option for building a skyscraper.

And it goes without saying, steel won't cut it either, as "inert" as it may be it will eventually give in to weathering, corrosion, and whatnot. Some precious metals are very resistant chemically, but their mechanical properties are not suited for the task, not to mention their rarity and cost.

Plastic, albeit an environmental disaster due to the time it takes to decompose, is not an option either - it will weather, it will degrade and it will fail. Not to mention it is flammable. It will make for a hell of a torch and subsequently an infernal lake of liquid burning plastic. Plastic might be used to encase steel frames, which will protect the steel from the elements for a while, but only until the plastic weathers to the point of cracking. Also plastic is usually soft, so any abrasive particles in the air would affect it.

You basically don't want to use for a skyscraper anything other than steel frame structure. Not for skyscrapers are we understand the term today, much less compared to some futuristic standards. Definitely not concrete. The big challenge here is protecting steel from corrosion. Corrosion resistant alloys get you only halfway. Paint will weather and crack, a plastic coating will weather and crack. Steel must be protected by something that is:

• moisture resistant and water repellent
• fireproof
• resistant to weathering and corrosion
• hard enough to withstand wind abrasion
• flexible enough to not crack and crumble as the structure flexes due to winds, quakes, and thermal expansion/contraction and as in time sags, which it will

Extreme density rock wool comes to mind here. It can be infused with steel frames in the early production stage at a molecular level, when the steel is still red hot, using an extrusion process. It can be treated with mineral oils to protect from moisture, and its external layer can be partially molten to form a hard protective crust. Granted, oil will eventually weather off, but that can be fixed by providing extra oil in reservoirs so that oil content can be replenished through gravity and capillary action. Even at high density, the wool will not be a rigid solid internally, and while the outside will inevitably crack in time, it will not crumble as the fiber will be holding it together. The purpose of the external shell is only to protect from abrasive winds and wool disintegration, the mineral oil on the inside is what protects from corrosion. Mineral wool is also a great insulator, which will reduce the severity of thermal stresses, it is cheap, abundant and recyclable. The steel structure itself must not use any bolts or welds but instead be held together entirely by a modular construction and its weight.

Earthquakes are the big obstacle to using materials, which would otherwise be good candidates due to their resistance to weathering. But if you are willing to go offshore, and of solid ground, you could have floating megastructures that would be immune to quakes. Granted, they won't be skyscrapers in the context of towers, more like floating bubbles, but they could get to formidable proportions. It is doable through additive manufacturing. The material could be tempered glass. Such a bubble will have the advantage of encapsulating a huge amount of space, providing natural sunlight, and creating the conditions to have an entire ecosystem isolated from the outside world, meaning that it could potentially survive a broad range of disasters, basically everything aside from a dense and continuous comet shower. Artificial lighting could even help sustain the ecosystem in the event of a temporary solar blackout, in the case of global volcanic eruption or nuclear winter. At that scale of construction, tsunamis will have the destructiveness taken out of them, using nuclear reactors the structure will be able to sustain life for hundreds or even thousands of years in a world that is otherwise inhospitable to life. Measures must be taken not to hit rock or get beached, that can be achieved either by anchoring somewhere in oceans' dead spots (plenty of floating plastic there that can be recycled as well) or by making the structure capable of sailing, and in case of loss of occupants, equip it with an auto-pilot software that will keep it off the shores by using nuclear reactors or renewable power sources.

Now if we get maintenance back into the equation, it should at least theoretically be possible to make a skyscraper that can last 10k years. It doesn't have to be human maintenance though, it could be a team of robots, which use renewable power and have enough materials to self-produce for 10k years. That's at least somewhat plausible.

The other viable option, a little more in the sci-fi realm, but still somewhat conceivable would be an engineered artificial life organism, something like a mega tree, but more resilient to the elements and elementals. It will essentially be self-maintaining, replacing weathered and compromised material at the nano-scale level, pretty much the organic version of the "robot maintenance" version above. However, that would be quite challenging, creating artificial and fully functional life aside, it will also have to be:

• immune to time, effectively immortal
• immune to fire
• immune to extremely hot and extremely cold
• immune to arid or wet climate
• immune to diseases as in system malfunctions
• immune to pH imbalances
• immune to full solar blackouts
• immune to viral and bacterial infections
• immune to a wide range of pests, from bacteria through termites, cockroaches, rats and everything that may eat it

Those challenges aside, if we presume that this is doable, such an organism can be employed into a variety of beneficial ways, for example, grow food, purify toxic water and air for the inhabitants, even grow electronic circuits, computers and communication systems and whatnot.

Answer 9

As others have said, it depends on how flexible your definition of "skyscraper" is.

Essentially, the problem of maximizing the lifespan of a structure comes down to three factors: Environmental stresses, surface area versus volume, and gravity.

1. The quieter the environment, the less stresses the structure is subject to.
2. The less surface area is exposed to the environment, the less damage the structure will accrue.
3. The less gravity, the less a structure has to continuously bear the stress of its own weight, eventually leading to cracks, buckling, and breakup. Of course, the only way to reduce gravity is to launch into space, which is its own kind of solution.

Problem #1 can be mitigated by careful placement. The ideals are:

• Dry weather: Low erosion/water damage.
• Stable temperature: Low thermal/expansion stresses on the structural material.
• Far from fault lines: Low earthquake damage.

If you're willing to sacrifice the visibility of your structure, building it underground may be a worthwhile investment. (People might not see it immediately, but once they do...)

Ancient pyramids solve Problem #2 by having almost no empty space inside of them. Modern skyscrapers are built to be weight-optimized to support the largest amount of useful equipment and people with the lowest amount of structural weight; this means that once a few critical elements fail, the rest of the structure is in serious jeopardy. A pyramid is almost completely made out of rock holding up more rock, so it has plenty of extra material to help keep its shape through the ages. A tiny bunker deep in the interior of the building can keep some stuff safe for millennia, in this way.

Problem #3 will only be completely solved by a "skyscraper" in space, specifically on an asteroid. As Thucydides mentioned, the Moon is also a nearly ideal place to build -- no atmosphere to cause trouble, seismic activity has long ceased, and very low gravity, although not negligible. But you could probably build something much more like a skyscraper in space, with lots of stuff inside, and get away with it lasting tens of thousands of years or more. Cover it in 5-10m thick of dirt, and you should be safe from more or less any micrometeorite damage (5-10m is about the thickness of lunar regolith, which is the layer of the Lunar surface that has been pulverized to dirt by micrometeorites).

We already have built skyscrapers in space. The height of a floor in a commercial building is commonly around 2.5 meters. All rockets built to launch humans are over 30 meters tall, or 12 floors high. The Mir space station was about 12x12x12 stories in dimensions. And the ISS measures roughly 110m by 70m in width, or 44 stories by 28 stories. For reference, a 40-story building looks like this. The ISS would decay out of low Earth orbit in less than a decade due to air resistance if it were abandoned, but such a large structure farther away from Earth could easily last millennia or more.

Answer 10

1. Like all real estate, location, location , location. You want a location that won't be hit by the next ice age nor seismic activity. Probably, building it far out in the mid-Pacific sea bed would be best, followed by the south central areas of Eurasia.

2. Skyscrapers are named after the top-most part of the mast of high sail clipper ships, so by definition, they should have a significant taller than wide outline.

3. The most industructable material known is Zircon which is so incompressible and non-abrading that crystals survive multiple trips through the tectonic cycle, being sub-ducted, then spit back out as in lava or metamorphic rock and then repeating the whole thing hundreds of times. Only the radioisotopes inside them cause them to degrade. They're the primary means of dating in geology. If you coated everything in the skyscraper with few millimeters of artificial Zircon, nothing would abrade, erode or catch fire. I don't know if the Zircon is itself structurally strong enough to make an entire structure with (the existing crystals are measured in millimeters) but if so, that would solve you're entire problem. More likely, it will just be an indestructible coating

4. Lighting is the major threat to skyscrapers. The "lightening rods" in them are actually huge systems of spikes, conductive wire, redundant systems and some seriously deep grounding spikes. You'd likely need a very tough standard temperature superconductor to handle the lighting.

5. But probably in the end, you'll need some kind of dynamic entropic flow structure, one that it held up by a constant energy flow that increases entropy so the 2nd law holds it together (that's how life on earth works). So, a very deep, geothermal system spreading for kilometers down and around the structure would provide the constant energy flow from the heat of the earth out into space. Diamond is the best thermal conductor BTW. Simple thermoelectric generators made of wires woven in through the structure from the tap root to the tip-top would convert the constant flow of heat, into a flow of current, which by the positioning of the wires, produce a constant repelling force, like a stack of electro-magnets that make a tower. If you had high temperature super-conductor, the magnets would be very strong and need only a trickle feed to produce magnetic fields for thousands of years. The magnets could be arraigned such that they repelled up and down but attracted in and out. If the structure did take damage e.g. a meteorite, the damaged pieces would be pulled back into a supporting configuration. (This based on a concept of space elevator some NASA guys works out some years ago.)

6. We're talking lots of power here. The skyscrapper's other structural material would act more like a rope holding the thing down that supporting against gravity. As such it could be made from almost anything not strongly magnetic e.g. titanium, which is functionally immortal itself. Lighter than aluminum, stronger than steel, doesn't corrode nor electro weld. If you could control the lighting, you could probably make the sky scrapper out of it.

7. You could even go the other way completely and make it an abandoned space elevator. A lot of the same techniques I mentioned above but since the thing will be a big cable with a mass stretching it out in space, things like earthquakes or gravitational collapse would cease to be a problem.

Answer 11

Could we build a skyscraper to last 10,000 years with no maintenance? Probably. See http://longnow.org/clock/ for a related project that's really kind of cool. Casting skyscrapers out of molten rock (basalt might be a good choice, it's pretty durable) or similar techniques would have a lot of potential.

Will we build such structures in any significant quantity? Doubtful -- they're expensive and our current structural needs tend to be obsolete long before the buildings wear out. You'd have to have a reason to want that kind of longevity before you started. Long-lasting materials are harder to work with and more expensive than what we tend to use, and we have no reason to use them in most cases since, if there's nobody to do maintenance, there's also nobody to care if the building falls down.

That said, in another 30-50 years, we might well have buildings that could last forever. Not because they'd need no maintenance, but because our robotics technology is advancing rapidly. If it becomes common for maintenance of skyscrapers to be handled entirely by robots, and if the maintenance of the robots can likewise be handled by robots, then the only limiting factor to the building's lifespan would be cataclysmic events that exceed its structural specifications, and the stockpile of energy and materials the robots have to work with. The skyscrapers most likely to survive would be the manufacturing plants where robot parts are made, since they'd (potentially) have a ready supply of raw materials and the tools needed to convert them into maintenance drones. If the build orders got cut off, it's conceivable that the remaining material stockpile would be sufficient to perform basic maintenance for a very long time. If the robots are networked and capable of finding new sources of raw materials on their own, whole cities might survive for millennia as well.

Answer 12

Build a bunker.

I'm talking cold-war-era-like, 20-stories-underground bunkers with included vertical missile silos.

Why bunkers are good candidates:

• These things are built to last, and to withstand enormous amounts of damage while keeping structurally sound.
• Unlike residential or commercial skyscrapers, bunkers are built with resistant materials. You can assume that state-of-the-art five-meter-thick nanolathed concrete will be used.
• They have both livable areas with low ceilings and awe-inspiring 100-meter-high vertical silos.
• If you assume a high-tech cold-war setting, then the military powers could build hundreds, even thousands of these things, and spend tons of R&D on making them lasting.

Why bunkers are bad candidates:

• They are underground, so they're not visible, so they're not awe-inspiring. D'oh.

Sometime after, there is some kind of cataclysm (haven't worked out an appropriate one yet).

Well, there's your answer to the problem of bunkers being underground. If you were to have a big flood, or any other kind of environmental event that erodes away the soft soil around the bunker, then the structures would just appear.

Granted, the structural integrity of an underground bunker is provided by the earth/rock/soil around it. But if you assume that the warmongers built a dozen hundred silo bunkers, it's plausible that just a few of them were built in a place where the erosion would leave them standing.

Answer 13

At first, I wanted to recommend artificial diamond, but after reading some comments (basically saying that it's too fragile) I thought why not use some other huge molecule (probably mostly out of carbon)?

Another option would be to use something similar to natural rock, but have some sort of living creature on the surface to help repair damaged parts. An example would shellfish, that's shell (very slowly) decomposes into chalk/limestone (the time-scale would not make it an ideal building material).

EDIT(from comments):

You would have a possibly alive thing/very complex molecule/mixture of chemicals that is put under the outer layer of the building, and if that layer is damaged, it gets exposed to air and sunlight, and using something slightly similar to photosynthesis it turns them into the material (probably organic) that the outer layer is made of. The clever bit is that only the outer bit is exposed to all the needed ingredients, and so only that makes more material.

Answer 14

Build it as a single crystal diamond.

It is possible. You can make small amounts of diamonds in your microwave using carbondioxide and hydrogen. It is a slow and an inefficient process.

Since the whole structure deposited layer by layer (in atomic scale) it is much like an additive manufacturing (3D printing).

Required construction time and energy is enermous today's standarts(I guess that's the semi futuristic part).

But the final structure: billion-carat-tower will surely be inspiring...

Answer 15

Woven carbon nanotubes are an option. There is an international race currently to get their manufacturing costs down and I fully expect it used as a building material in the foreseeable future. There is even a proposal to build a massive air cleaning factory that sucks in CO2 and converts it into CNTs. http://phys.org/news/2016-06-power-co2-emissions-carbon-nanotubes.html

CNTs are strong enough to be used in a space elevator so a "mere" skyscraper should last that long. Especially if it's built solidly, with that purpose in mind, using all of the best techniques and other special/new materials like the various ceramics with crazy properties.

Answer 16

I'm taking the unusual step of putting in a second answer because it is more than an edit of the existing answer and also building on some suggestions in the comments.

Building a skyscraper or anything else on the Moon means a lifespan of millions of years as a recognizable artifact. Some comments mentioned building a "Great Wall of Luna", which would be both large enough to resist erosion by micrometers for eons and visible from Earth. While megalomaniac emperors throughout history have wanted to build monuments that last forever, few succeed. Building a mammoth wall on the Moon also seems a bit pointless, until I stumbled across this.

The The Friedlander Cold Crown is simply a giant circular wall surrounding the lunar pole (or poles) to create a shadowed area where gasses from lunar industry would condense and freeze, maintaining a very hard vacuum on the lunar surface. Even molecules of atomic oxygen moving across the lunar surface as a result of lunar mining or industrial processes would be fantastically corrosive and damaging to industrial and scientific equipment (imagine a massive lunar telescope who's mirror was pitted by corrosion due to oxygen venting).

The takeout for this is oxygen (primary waste gas from lunar rock refining) can travel around the moon in around 47 hours (450 hops at 160 km each, taking 380 seconds between bounces)

The Cold Trap is a circular wall 40 kilometres tall that surrounds the poles, and any molecules of gas which fall into the trap radiate their energy away and do not get new energy from the Sun. From the Earth it may look a bit like this:

The Friedlander Cold Crown

So we have a plausible reason to build a megastructure which is both visible from Earth, built in a "quiet" area devoid of most environmental issues and capable of resisting erosion for geological ages, most likely still large enough to be visible a billion years in the future when the Earth becomes too hot for water based life....

Answer 17

I don't think I can make it to 10,000 years, but here is how I would try to make a long lived building that was usable.

Let's make it the height of a clipper ships masts. Since power may be intermittent, call it 15 stories, Who wants to walk up an 80 story building? 160 feet, 50 meters.

The steel frame is made of Corten steel or some equivalent. This when exposed to water forms a fixed layer of oxide that protects the rest of the steel from corrosion. Steel is not exposed, but is embedded in the concrete. We don't want a repeat of the Building 7 collapse from the building contents burning.

Concrete rebar is also made of self limiting corrosion steel. Prolonged wet exposure won't cause the rebar to rust then crack the concrete.

All floors have a slope to them so water exits the building at scuppers/spouts. (The building could look like it's studded with gargoyles.

Windows have heavy lintels and are set back so that even a missing window results it little water ingress.

Windows are made of synthetic sapphire.

Building is clad with synthetic sapphire, done in overlapping shingles so that hte connecting mechanism is not exposed. This is the anti-abrasion layer. The cladding can be coloured by use of impurities. (ruby, blue sapphire...) Note: Potential problem of people stripping off this layer for ornamental use, much as the marble was stripped off the pyramids. For this reason, the cladding should not be polished but should be flat black at least at the lower levels. It may be possible to develop a sapphire solar cell for cladding the southern side of the upper floors to provide some interior power.

It may be that a cladding of sapphire and carbon black would work better, both for expense and for shatter resistance.

Being black, the building will be warmer than the environment. Harness this for passive stack ventilation.

Initial interior would be open design broken by columns. This allows some use of the building even without power, and helps with ventilation. Over time, different groups would partition it differently, but partitions are regarded as furniture, not as the building proper.

Wear surfaces are sapphire again. Floors are sapphire tiles set into concrete.

Doors have aluminum or non-corrodable steel frames. Hinges and hinge connectors are engineered for 100 times a day use for 10,000 years. (In my years doing building maintenance, it's not the hinge that fails, but the fastening to the door or jamb.

Automatic closers. Hmm. These have a definite life span. It may be better to make doors sliding doors on a sloped track so that gravity is responsible for closing the door. They could be jammed open, but would resume function when the jam is removed. Convention doors could be used wherever a non-auto closing door is needed.

Utilities: I'm much less confident in 10,000 year life span. Our chem department at University had glass plumping from the lab sinks. You certainly win with corrosion resistance there, but joints were made with stainless steel clamps and some kind of gasket. Part of building longevity is to make the inner systems accessible. Ships are designed to be maintained. You see the bones as you walk through them. Houses are not. So wiring is in channels, not in the wall. Water supply is plastic, place where it won't be exposed to UV, and sized large enough that flow erosion is small. Valves. How do you build a dripless faucet that will last 10,000 years?

Some longevity can be gained with redundant systems. Warships have a main power bus ring, and sometimes two on different levels. Breaking the ring at any one point still leaves power to the rest of the ring. Isolation breakers keep a shorted bus from taking out the whole bus. This mindset can be applied to plumbing and data too.

Answer 18

Give it some form of automated maintenance. Alternatively, an engineered species of lichen or coral-like organism could keep a mineral based structure in good repair and vastly extend its lifespan. Living things can repair the minor day to day damage that usually takes down large structures. Once they have some form of maintenance then all you need is fairly benign location and decent structural engineering.

You could also use trees, redwoods actually form buttresses joining one tree to its neighbors. If they were engineered trees some of them surviving for tens of thousands of years is not out of the question. Imagine your explorers realizing the forest they are in is really a housing development.

Answer 19

If it's OK to repurpose rather than build from scratch, then it must be tepui FTW. Mount Roraima in particular: 2338m prominence (935 stories?), 31 km^2 flat summit area, and it's already about 2,000,000,000 years old. It even has caves.

Answer 20

10.000 or 100.000 or 1 Million year old skyscraper would be no problem. Also wood could be possible for construction, if you renovate it in depending of the material qualities like Japanese Temple do since centuries, only made by wood without glass and without metals. The main thing will be, the social system, who care about your building. You will need a believe or in old words, a religions system, who care about themselves in a nice and harmonious way for your plan of 10.000 or 100.000 or the 1 Million year old building. Every plan begins with good idea and plan. The matrix and material for the building will not be the problem of first step. First find in your brain a human system who will carry your idea over centuries, to love your idea by the avatar of your building and run for you. They scientists in 1.000 or 100.000 or 1 Million, which will love your idea and your building, will always find the best way and materials for keep it proper and fresh, your building. Feed them by your first idea and they will run for you, as long your building will stay on earth.

Answer 21

I like where Rat In A Hat is going. As population increases and efforts like the International Space Station continue to succeed, I could see large scale apartment or business structures in Earth orbit. If Shock & Awe (tm) are what you are after, only one or two need to make landfall intact. In this scenario, building on Thucydides answer, we utilize the advantages of space for longevity. We also assume there are automatic safety measures in place for if the structure fell out of orbit to bring it back to the surface allowing the most survivors possible within and without. Whatever event reset life on earth, the supply line was cut and there is none left onboard. Depending on your story needs, they current Earth inhabitants either see it land, or discover one that has recently.

Answer 22

If you mean by without maintenance really means is without human maintenance: then how if you build a forever learning and adaptable ai that can maintain and update itself included in the structure. At first it can deploy a not far future drones to maintain the system and building and later can upgrade itself, learn and discover more technologies, even search and harvest materials it needed from the nature far after human had no longer existed. There's one beautiful story involving a structure like this as its 'main character' its a manga by Boichi https://myanimelist.net/manga/2436/Hotel

Answer 23

As mentionned, pyramids lasted very long mostly thanks to their shape. A tetrahedron is much better than a cube (skyscrapers). However it s not the optimal shape. Basically whenever you have edges, the edge will wear down faster then the other parts and thus will weaken the structure.

The optimal shape is semi sphere. Any material like concrete will be fine. A semi spherical concrete bunker would probably last 10,000 years.

After 10,000 years, wind/corrosion/rain will have worn it down and it ll look like a small rocky mound with probably some grass on it but it ll still be there.