Otdfbt

Most "ancient artifact" stories come from the "atlantian" theory: a civilization that advanced much farther than we did, but at some point collapsed and dissapeared.

Call them Atlants, Elves, Gods, but in general these artifacts tend to be made to much better tolerances and materials than current era artifacts.

To put an example. Let's say our current society collapses and 2000 years later, humanity has been able to rebuild to middle-ages tech. Imagine some farmer, ploughing a new field, unearths a ceramic kitchen knife. The plastic hilt almost intact, and the edge so sharp it blunted the crude iron hoe he was wielding.

For us, it was a disposable kitchen knife. For him, it netted a nice reward from the local lord, who in turn presented it to the local king, who probably decided the best use was to attach it to a pole and make the kitchenette polearm, a fearsome artifact from ages past.

The other explanation is the "magical artifact". In a world where magic is real, most of the time magic artifacts grow more powerful over time. Like the magic capabilities of the artifact are not fully revealed until it is given time to mature... centuries and centuries.

Answering the question put in the comments:
As for artifacts that we can use... the industrial processes have made us forget a lot of oldTech, specially oldTech that is not mass scalable or simply we don't have an use right now. For example, I did some research on bronze-age china, and we don't know much about how they forged the swords. We know they covered with certain chemicals to make them more durable, and that it was not a random process, but the lack of books makes very difficult to ascertain HOW they did it, and while we can replicate some of the processes... we simply don't know how to do them without "cheating"

For a real life example:

The fabled sword of goujian was found intact even though it was submerged in water for almost 2500 years. It is suspected that the airtight lacquer covering and the chemical composition of the surface layer of the sword preserved it. I can replicate this surface covering using modern techniques, like vacuum sputtering, but this is a modern method, quite expensive, and does not tell me how they did it. So if we wanted to make more durable bronzes, it would be interesting to investigate how they made it, but we don't, because we don't need durable bronzes: we have other materials that fill the gap and are readily available and cheap.

For another real life example, hinted in the comments:

It is known that roman concrete is superior to our common Portland concrete in several aspects, but specially:

• It is allegedly cheaper to make, and more ecologic.


• It has a very superior performance on marine underwater situations. We have uncovered 2000 year old underwater structures intact. Portland does not fare very well on those situations.

For many centuries we ignored roman concrete, because most other concrete bindings use volcanic ash and britain (where portland was invented) had little. But the demand for concrete is so big that not only the ecologic impact is starting to be too important to ignore, the materials needed to make Portland are starting to become scarce.

So there is a very renewed interest in reviving the techniques needed to make roman concrete, and finding suitable replacements for the materials that are not as easily available (such as volcanic pumice).

Knowledge

For the latest things, sure, modern is better. But think of something old fashioned, like a chariot or some building techniques: if we no longer have the knowledge on how to do it, they are of course better. Just to give you an example, there is still lack of consensus on how did Brunelleschi managed to build the dome in Florence, yet we can build 800 meters tall skyscrapers.

For most of the middle age anything that the Roman Empire built was simply too advanced to be replicated, so, if the level of knowledge falls down, older is better.

"Ignorance" of the maker

In the past, when the engineering knowledge was necessarily less advanced, any good engineer just supplied to it with a generous amount of safety factors in the design. Those larger safety factors made the product necessarily more sturdy. For example, I still have the garden scissors my grandfather used when he worked in his youth, 90 years ago. I never managed to find a modern garden scissor lasting even 1/9 of that.

We've only just, in literally the last couple of years, been able to replicate the steel used for the Vikings' Ulfberht swords. A rather eccentric farrier from the US by the name of Al Pendray finally cracked it not long before he died in 2017. That steel is superior to anything we can make today not because it has any one quality (hardness, durability, strength, flexibility) that's better than a steel we can make but because it has levels of all those qualities that we can't create in combination using modern mass production techniques. Making Wootz involves an expensive technique that, at this time, cannot be replicated on a large scale, it also involves a piece of very particular and quite peculiar chemistry involving Vanadium that's only been very recently understood. There's also the legendary flexible glass of Rome an invention that got it's maker killed and which has, probably, never been replicated. So sometimes the ancients understood a trick or two that we don't.

As to why ancient artifacts in story and myth have such power, that is often based in one of two ideas, the first we'll call the "Hyborian Age thesis" and the second the "accumulation argument":

The Hyborian Age thesis goes like this; once long ages ago there was a great and powerful civisation that knew all sorts of things we didn't, especially magic and/or technology that conforms to Clarke's Third Law and crafted powerful tools and weapons that beggar modern belief and knowledge. There are many examples of this in fantasy, any of the ancient swords in the Hobbit/Lord of the Rings whether made by Men or Elves, The Scar's Probable Sword (a personal favourite), Amber's Spikards and any time anyone ever invokes the word Atlantis to explain something extraordinary.

The Accumulation Argument is a little different here's several versions;

• Version one goes something like this: objects are just objects but the older an object is the more it has done and the more notoriety, and therefore power, attaches to it. Such objects, be they weapons, tools or armour, are awesome because and only because they are ancient and have been around when stuff happened. The only example I can think of off the top of my head is the Armour of Bronze from David Gemmell's Drenai Cycle everyone thinks it is magical and it's been on battlefields where the apparently miraculous happened for generations so it is somewhat magical in it's effect on people who see it on the field of battle. A possible second example may come from The Dresden Files' treatment of necromancy.


• Version two deals with the concept of "sacredness" for lack of a better term. Basically the more an object is used for a given task in the name of a given cause, whether that cause is conventionally religious or otherwise, the more belief in the power of that object grows and the more real power it has to serve the cause. This can be couched in positive terms, i.e. believers in the power of the object and the cause give it power to do the otherwise impossible or more negatively, unbelievers fear of the weapon give it power over them, or both, often both.


• Finally there is an actual accumulation of power, the object was not originally terribly powerful but it has the ability to accumulate power slowly over time, this can mean that a user or even successive users deliberately imbue it with more energy (as with Shilly's staff in Sean Williams' Cataclysm series) or it can be the passive uptake of some sort of ambient power.

Falls of civilisations and subsequent dark ages

I have no real evidence for it, but I suspect the trope likely stems from the collective European memory of the collapse of Rome and the Dark Ages that followed. Cultures remembered (or read) how advanced the ancient world was compared to their current state. Thus 'old stuff is better than current stuff'. This lasted as a reality for a little while, but lingered as an impression for far longer.

If you want a more low-fantasy take on this, your culture needs a pretty hefty Fall and subsequent Dark Age. Set your story within that dark age and you can plausibly have 'ancient powerful artefacts'. This works best over a period of a couple of hundred years though, not thousands. Artefacts degrade, new technology develops. It's not a stable state of affairs.

Another realistic alternative is that people believe these ancient artefacts are more powerful, but the truth varies considerably. They have romanticised the past based on scant information, and paint a picture of their mighty forebears as unimaginably powerful when in reality they're not too dissimilar from how they are now. Some technologies have been lost, but others have been developed. Progress has resumed, but the impression remains. This would be more realistic over a period of a thousand+ years, judging by Western history.

Edit

@John pointed out an even better example with the Bronze Age collapse, which resulted in/caused the destruction of early European advanced civilisation and the long-distance trade routes it maintained.

One of the reasons this works better is that bronze artefacts survive far better than iron ones. Bury an iron sword in a bog for 100 years and it'll be junk when you pull it out. Bury a bronze sword in a bog for 100 years and it'll still be deadly.

If you lose the ability to make bronze (either from loss of knowledge, or loss of the trade routes that shipped tin from Cornwall all the way to the Middle East), you could legitimately find superior weaponry buried in the ground.

There are many reasons why old stuff can be better than new stuff

In addiction to the most popular answers, I can point some other interesting reasons why it could be impossible to build today something that is equal or superior to the old things:

• Extinction: a tree, or an animal, from which a particular product was made, has gone extinct. For instance, some recipes of Roman cuisine are impossible to replicate because they required an extinct plant. So, if an effective medicine or a spell (in case of a magic world) would need an extinct plant, it is clear that the new products can't replicate the good old stuff.


• Environmental changes: another interesting story is that all steel manufactured after the 40s is slightly radioactive because of nuclear tests in the atmosphere. In other words, for some purposes, like very sensitive measures of radioactivity, whatever steel is built today would just introduce too much noise to allow for the construction of a precise radiation detector. You can replicate something similar in your world: think of a powerful world enchantment that makes all iron alloy impossible to heat, so that it is physically impossible to forge new swords and shields, and the old ones become increasingly more valuable and prized.


• Economy: it is impossible to replicate the reasons (social, religious, economical) behind some of the biggest masterpieces of past history. An artist could no more be able to dedicate all of his life to painting or writing a single piece, or you could no more find hundreds of people (and the necessary funds) necessary to build a pyramid. Clearly, machines would allow to reduce the needed resources, but you would lose the "hand-made" feeling behind the equivalent works of the past.

Selection bias

Something 10,000 years old, has lasted 10,000 years. Most things we have today wouldn't last nearly that long, and certainly wouldn't in the original condition.

Of the millions of swords made in a particular era - just one of them turned out perfect. It didn't tarnish, didn't degrade, and was an elegant and excellent enough weapon that it stayed an important status symbol, handed on to significant individuals through history.

That goes double in a setting where 'mystical technique' or 'magic' applies.

This one sword was the magnum opus of 40 years of being a master swordmaker. Intended as a gift for a warrior prince, who would truly appreciate a sword of exceptional quality. It took 666 days of unceasing labour, and repeated folding and reforging. It took the last grains of metal from a fallen meteor, and quenching in the blood of dragons. Or if not fantasy, maybe just the last of a batch of particularly good composite steel, with 'just right' mix of carbon and iron - that was proven over years, and set aside for a special occasion.

It's not that craftsmen were better 'back then' - it's just that you've a much larger pool, and a way of 'filtering out' the worse quality items, because they just didn't last.

Firstly, it's not correct to just dump everything old into a "shistory" category. There are plenty of ancient things that are amazing and cannot be reproduced today. Artifacts that have survived so long usually do so due to their high quality, either physically (pyramids) or intricate enough to be carefully preserved (crowns and other jewelry).

Maybe not stone-age artifacts, but musical instruments can be several hundred years old, and cost an absolute fortune. The same with paintings. For some cases it's the particular craftsman, painter, sculptor who has never been equaled since. Mostly its that the market for quality goods is no longer viable for individual artists.

If you look at modern mass-production methods, it's all about reducing item production cost to maximize profit. A good product can be initially launched to a reasonable price, as novelty sells, but as time goes by, the production gets optimized, replacing expensive parts with cheaper ones, skimping on quality control tests, and using cheaper methods of assembly. The actual quality gets shaved off, and the saved cash goes in the company pocket. Companies also make more if the product needs to be replaced, too, so there's little in it for them to build solid, lasting, high quality products. This is known as designed obsolescence.

Work done by individuals, or boutique companies cannot compete on price, availability, time-to-market, or just marketing and advertising in general, so we see a massive change in how goods are actually produced.

Industrial production in capitalistic society is a recent invention, and has caused a massive decline in handcrafted work. Prior to a hundred years ago, goods were always hand crafted, and the better quality artisans would spend their life perfecting their craft, and charge more money for their superior quality goods. The absolute cream of the crop would work for kings and noblemen, supported by royal budgets or arts patronages. Quality and prestige were part of the product the customers paid for.

Today, its mostly just cheap Chinese imports that fall apart after a short while, forcing you to buy another. And in today's economic climate, that is the method which works best. The drawback is everything is plastic and shitty, and little of it will be around in 10 years, never mind 1000.

I can think of some other ancient artifacts which have not been equaled, or cannot be produced today. Look at the Book of Kells (https://en.wikipedia.org/wiki/Book_of_Kells) and ask yourself if a team of people could today dedicate their entire lives to hand-coloring a single book (one copy only). It just can't happen today. There are many other examples of religious artifacts surviving over 1000 years, many of which would be difficult to produce today, and impossible to produce in the same way using the same techniques. What about the cathedrals (Notre Dame being in the news recently)... you can't build one of those anymore, it's simply not economically and politically justifiable. Restore it, sure, but build a new one? No way.

Some artifacts are non-physical, and still preserved for thousands of years. There's the story of Christ, or the entire Bible, and whether you believe or not, it should be recognized as one of the more well-known and preserved stories of the last few thousand years. And its in large part due to it being a very good story, and not much has come along to top it. (Romeo and Juliet, 400 years old, many other examples like Little Red Riding Hood, etc)

Other things have also stood the test of time, like Chess and Go, military tactics, discoveries and inventions in mathematics, etc. I wouldn't exactly call them artifacts but they survive because they haven't been bettered.

Finally, the real reason old stuff is good, is that all the old stuff which wasn't good, was not worth saving. History and time have eaten up all the crap, leaving only the shining awesome masterpieces.

There are 2 typical reasons why ancient artifacts are so valuable:

Everything was better in the past, especially magic

It's also a common pattern in nearly any imaginary world that "in ancient times magic was much more powerful than today".
In many fictional stories people lost the ability to utilize magic powers as well as their ancestors could or the knowledge about how to create powerful artifacts was lost over generations. The only way to obtain a seemingly otherwordly power is to obtain an item from a time when such powers weren't as otherwordly.

Different stories have different reasons for this decline in magic:

• Humans spread over the world and displaced the "old races" like elves and dwarves, who were much more adept in the arts of magic


• Humans lose their faith in the gods and they, in turn, lose the power to grant magic


• The world was filled with magic but now it's simply used up or the source of magic has become tainted

It's too expensive to create a copy

To keep some balance in a magical world, the creation of powerful artifacts requires very powerful beings and often some kind of valuable sacrifice (like a soul, a heart of a dragon, feather of phoenix or some obscure material no one knows exactly what it is). These resources might simply not exist (anymore?) or someone might not be ready to sacrifice their own live to create some magic wand they couldn't use anyway (since they're dead...). Searching for existing items is often the only solution.

Fundamentally it is about numbers.

Artefacts and relics are rare. This means that there is a low chance of someone or some event creating them. There is a low chance of someone or some event being capable of creating them as well.

These probabilities then go up with time, resources and number of people. This should be fairly self evident. If there is a certain chance that an event will create a relic, such events are more likely to happen over the past thousand years than in the next five seconds. If there is a certain chance to have a smith capable of making an artefact level magical sword a large empire with thousands of smiths has better odds than a village with one. If artefact requires expensive materials or processes, it is more likely to be created when the times are good.

There are also threshold effects. The canonical example are the European Middle-Ages where people simply did not have the resources to do things like the Romans before or the renaissance after them. Some things might require a level sophistication that requires specialization made only possible when the volumes are great enough. That one village smith is not going to be specialized making magical artefact swords, he is too busy making and fixing things people need to survive. If making the artefact requires a process taking a century it is unlikely to happen in a kingdom that only exists for one or two generations.

So how does this map to common fantasy?

Fantasy settings generally have histories spanning tens of thousands of years. Past empires often lasted for millennia. Especially if they were established by long lived races such as elves.

It should be fair to expect that your past Elven Empire that lasted ten millennia created more artefacts during that time than your current human kingdom that has existed for two centuries.

Similarly those histories are often filled with those powerful empires collapsing catastrophically. This is obviously based on the Roman Empire. And just as with Rome, those collapses were followed by reduced population densities and resource availability. Those past empires had much better odds and ability to create artefacts.

They would have more people with the skills needed, those people would have more specialized skills and education, and they would have worked with better resources.

This is incidentally where our modern sensibilities fail us. Our populations and economies have grown at insane rates during the last few centuries. Our experiences and the experiences of several preceding generations would have been the exact opposite of those in most fantasy settings and not really related to the resource and population constraints that are the historical norm.

We do not have better things than in the past because we live later. We have better things because we have more people and resources than ever before.

And it should be noted that because of those threshold effects these things almost work exponentially. Internet for example multiplies the ability of people to communicate and produce information but it or the technologies it needs are not going to be created unless people already produce enough information to need them. Economies of scale do work for effects of population and resources (and even time) on artefact creation.

I think the most simple answer is just "magic", and ignorance:

For one, during the last few centuries "magic" that was previously widely accepted to exist "disappeared" as science somewhat took its place. The coffee machine you use every morning would have been clearly "magic" just a few hundred years ago. But is it magic to you? - So, whatever advanced we encounter daily in our time was definitely magic in ancient times.

From there, it's only a small step to saying that there used to be magic in ancient times which is now gone.

And here comes ignorance into play. Through historical records, pictures, paintings, films,... we (believe to) have a pretty clear picture of what the world, and life, was like a hundred years ago. Or two hundred years ago. But the world of, say, 3000 years before our time is much less documented and thus by itself quite mysterious.

So we have a world about which we don't know much, where the existence of magic was wide-spread common sense, from which we may find a rare artifact.

Or, seen more pragmatically, if, as a world builder, we want something magic, where do we take it from in the most plausible (or easiest) way? How about a mysterious world which we have no access to, where magic is a common thing and from which artifacts can reach us without too much hassle (compared to, e.g., extra-terrestrial devices or things from the future)?

One could have some character craft something akin to magical in our time, but that is harder to make plausible because people have a grasp of what technology today can do. So instead of trying to create a somewhat credible background about why or how man's current capabilities enable something magic-like without violating what people know you can just take an artifact from some place about which the common person, or everybody, knows little except that it definitely exists.

(I deliberately used the present tense above to describe ancient times, because w.r.t. the (desired) effect the ancient world is a mystical world, perceived like a place you just can't go to.)