Why has so much magical knowledge been lost since ancient times?

Question

In the Harry Potter universe, the most powerful magical artifacts or spells all seem to be very old, while there seems to be no more powerful works of magic being created in modern times.

For example:

• The Philosopher's Stone, which can transmute any metal to gold and produce the Elixir of Life, which makes the drinker immortal. However, there is only one Philosopher's Stone (Flamel's not making another one), and that was made at least 500 years ago (Flamel celebrated his 665^th birthday before he died, and he would have had to create the Stone before he reached 165, as by that time he would be extremely old).
• The Resurrection Stone, created by Cadmus Peverell, had the ability to bring back an 'echo' of dead people. The only other way this is known to occur is with Priori Incantatem, where wands turned against other that share a core 'connect', and the one that loses the battle regurgitates it's last spells in reverse order. However, bringing up an 'echo' of people with Priori Incantatem only works if the losing wand has actually cast the spell that killed the people. This means that the Stone is very powerful, able to call up the 'echo' of any person ^{_{(I presume... I don't think there's canon stating that it can only call up those who the user knew)}}. This stone was created about 800 - 900 years ago, when Cadmus Peverell was alive (yes, the question refers to Ignotus Peverell, but they were brothers and they worked on the Hallows together).
• The Elder Wand was the ultimate wand of power (hey... it repaired Harry's wand when nothing else would), as well as having accumulated wisdom through the ages. This was made by Antioch Peverell, also about 800 - 900 years ago.
• The Cloak of Invisibility was the invisibility cloak, made by Ignotus Peverell 800 - 900 years ago.

  Ah, but the Third Hallows is the true Cloak of Invisibility, Miss Granger! I mean to say, it is not a traveling cloak imbued with a Disillusionment Charm, or carrying a Bedazzling Hex or else woven from Demiguise hair, which will hide one initially but fade with the years until it turns opaque. We are talking about a cloak that really and truly renders the wearer completely invisible, and endures eternally, giving constant and impenetrable concealment, no matter what spells are cast at it. How many cloaks have you ever seen like that, Miss Granger?

• Hogwarts. Creating a semi-sentient castle with moving stairways and various other massive enduring enchantments (for example, the ceiling) is no mean feat. This was created by the four founders (Godric Gryffindor, Salazar Slytherin, Helga Hufflepuff and Rowena Ravenclaw) "over a thousand years ago", although the exact date is unknown.
• Horcruxes are cursed objects that contain a 'consciousness backup' that prevent actual death as long as they exist. Created by Herpo the Foul more than 2000 years ago, they are indisputably evil, but also indisputably magically powerful.

Whereas in modern times, the most powerful magical artifacts or spells seem to be all products of Weasley's Wizarding Wheezes, staffed by a pair of drop-out mischief-makers.

Also, no-one is able to recreate any of the artifacts, otherwise they would have, as they are highly desirable items.

This is totally different to Muggle history, which is one of increasingly powerful inventions and discoveries. Sure... there's still pyramids in Egypt that we don't know how they were built at the level of technology of the builders thousands of years ago, but if we wanted to, we could recreate them with our level of technology... faster.

However, modern wizards don't know how the artifacts were created with the level of technology of the ancient wizards, and they are unable to recreate them with their current level of technology.

There seems to be a lot of magical knowledge lost over the years, leading to a decrease in the power of magical creations. Why was this knowledge lost?

(It's not because of the HPMOR Interdict of Merlin...)

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tl;dr

Ancient wizards made really powerful things. Modern wizards don't and can't make similar really powerful things.

There's obviously been a loss of magical knowledge.

What is the reason for this loss?

Answer 1

I'm not an expert of History of Magic, but I'll do my best.

In the beginning, say before 900 - 1000 A.D., the wizarding community lived peacefully with Muggles.

Especially before the widespread diffusion of Christianity, magic was an important component in some religions, to the point that several cultures included a god/goddess of magic: Hecate in Greek mythology, Isis for the Egyptians, and so on. It is likely that some priests were devoted to the specific cult of such divinities and, if this is the case, wizards were not only accepted, but also considered as very important people.

This means that wizards and witches were, at that time, absolutely free to experiment spells, potions, and the like, and in some cases even encouraged by the society (e.g. the Strengthening potion may have been used in the Sed festival, when the Egyptians performed a series of rituals in order to renew the Pharaoh's strength).

Between 900 and 1000 A.D., at least in Europe, Muggles start persecuting wizards, or at least don't tolerate them anymore. This is suggested (in-universe) by the fact that Hogwarts was founded in a remote region,

far from prying Muggle eyes

The Founders build Hogwarts, and magic is taught to the new generations. Given the remote location of the school, and the contemporary foundation of Hogsmeade, it seems likely that wizards lived in a close community somewhat next to Hogwarts. The close proximity of many wizards, and perhaps the need to update the magical knowledge transmitted to the students, contributed to intense magical research and development.

Out of universe: around 1144, an Arabic book on alchemy is translated in Latin by an English Arabist. This marks the beginning of a new wave of magical research, related to alchemy and also on potions, by well-known wizards such as Paracelsus.

The 12th century is a very important period in magical history, also because of the Peverell brothers (see Who came first; The Four Founders or the Peverell Brothers?).

Now, if we can compare Muggle and wizarding history, during this period the first (European) books on magic are published, probably by combining ancient manuscripts with personal experience of the authors.

This is a crucial period: the magical knowledge that is not written in the first books nor taught by the Founders is lost within a few centuries, because of the limitations of oral tradition and so on.

The 15th century marks the beginning of an intense period of persecution towards witches and wizards. Nearly two centuries later, wizards start thinking that something must be done in order to protect their world: they start to seclude themselves from Muggles and build a new society.

According to the Dumbledore's notes on The Tales of Beedle the Bard, the Department of Mysteries is founded in 1672 (if not earlier), thus predating the Ministry of Magic. The Unspeakables - if that was their original name - perform research on a wide variety of topics, including time, love and death.

The International Statute of Secrecy is signed in 1689, and officially established in 1692. Now, we don't know if a "law enforcement agency" existed to enforce the Statute, but this decree marks the definitive separation of the wizarding community from the Muggles.

In 1707, the Ministry of Magic is founded. Another crucial point: before the foundation of the Ministry of Magic, wizards lived - more or less clandestinely - together with Muggles, and thus they didn't need a proper occupation in the wizarding world. This means that they could experiment spell, potions, etc. during their spare time, without any legal or bureaucratic restriction.

Ever since its foundation, the Ministry of Magic became the most important institution in the wizarding community, not only from a political point of view.

It is estimated (Is there an estimate of how many people work for Ministry of Magic?) that, at the time of the events in the books, nearly 1000 wizards/witches out of 3000 worked for the Ministry. Most remaining adults have jobs connected with the Ministry and/or Hogwarts, such as Healers at St. Mungo or owners of shop in Diagon Alley, and children study at Hogwarts.

It seems reasonable to assume that this percentage of Ministry employees versus adult wizards remained more or less constant throughout the centuries. Ever since the foundation of the Ministry of Magic, a lot of adult wizards started working for the Ministry or Hogwarts, and as a result they had far less time to develop new spells, and so on.

But there is a much more important consideration: legal regulations.

The Ministry of Magic regulates every aspect of the wizarding life, including stuff like cauldron thickness. In particular, the Ministry not only forbids pre-existing spells, such as the Unforgivable Curses, but also restricts the development of new forms of magic.

Examples:

1. Ban on Experimental Breeding: restricts developments in topics related to Care of Magical Creatures
2. Registry of Proscribed Charmable Objects: restricts developments related to Charms

The only "wizarding research hub" is the Department of Mysteries, which performs classified research on fundamental topics, such as death, love, time and space.

It is unclear whether they only perform research or also development of new forms of magic, since the Veil was likely not created by the Unspeakables (see Who created the veil in the death chamber, and why?), but the Department of Mysteries may have invented the spell which automatically records the prophecies in the Hall.

The secrecy behind which operates the Department of Mysteries limits the knowledge of fundamental topics by lay wizards, who must obey the Ministry regulations and are thus limited in the type of magic they can develop.

In addition to that, the very fact that some types of magic cannot be developed bounds to secrecy the few wizards who intentionally violate the Ministry of Magic regulations, and I'm not only talking about Voldemort, but also about Hagrid (who, if it wasn't for Dumbledore, would have probably been taken to Azkaban).

The wizarding community can be classified in the following categories:

• People without the time and/or advanced knowledge needed to develop new magic (the Weasleys, the Malfoys,...)
• People with advanced knowledge of magic, who develop new magic in compliance with the Ministry regulations (Dumbledore, at least at the beginning, and possibly Snape), and can publicly transmit their knowledge
• People with advanced knowledge of magic, who develop new magic and don't care about the Ministry (evil wizards such as Voldemort,but also Hagrid), and thus cannot publicly transmit their knowledge

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tl;dr summary

Before the foundation of the Ministry of Magic, wizards had the time and the advanced knowledge (which disappeared in more recent times, if not written in books nor taught by the Founders) to develop new kinds of magic, without any legal restriction whatsoever.

Ever since 1707, most wizards have less time and advanced knowledge to perform researches about magic, and the few wizards who devote their time to advance magic either comply with the Ministry of Magic regulations or they risk to be brought to Azkaban. Those who illegally research magic cannot publicly describe their discoveries/inventions, or they would be prosecuted.

As a result, ancient magical knowledge has been lost and magical research and development is very limited.

Answer 2

First, the premise isn't entirely true

New and (at least moderately) powerful spells are invented frequently. Severus Snape, for example, invented Sectumsempra, a powerful curse that left wounds that were nearly impossible to heal. Tom Marvolo Riddle, alias Voldemort, seems to have discovered a potion that induced thirst and hallucinations, with no apparent antidote. As mentioned by Red_Devil226, we cannot forget the Wolfsbane potion, which allows a werewolf to keep their human mind and was developed in the 1970s.

Fred and George, who might be dismissed as pranksters, created an invisibility charm that extended beyond the boundaries of the charmed object. Not only did Hermione consider this impressive, but one might guess that Ignotus Peverell did not have access to this particular power. His Cloak only conceals that which it covers!
Powerful magic is still being developed. But in a plot with teenage wizards, preexisting spells or items will simply be more relevant to the plot than the frontiers of magical research.

On the subject of the frontiers of magical research, incidentally, let us note that the Department of Mysteries contained such powerful devices as a bell jar that could reverse time, a scale model of the solar system with realistic physics, and a portal to Death itself. All of these are the subjects of active magical research, and most likely have existed no longer than the foundation of the Ministry of Magic

But the point still stands

As previously mentioned, powerful magic, and indeed powerful artifacts, are still being developed. But even if it be a generalization to declare that ancient wizards produced more powerful magic, the question does remain: Why were the secrets of some of what they did invent lost?

• Horcruxes: The secrets of making Horcruxes were not lost at all. Many books on the process still existed as of Harry Potter's school years, with explicit instructions on this most evil of Dark Arts. Of course, the general process of splitting one's soul has remained unchanged for thousands of years, but why should this surprise us? So has the pulley, or the steam engine, or elementary geometry. Basic things stay basic.

• Hogwarts: There is simply no good reason to assume that modern-day wizards could not construct something like Hogwarts. The Founders had not only vast magical knowledge (for their time), but time. The construction of Hogwarts was a high priority, with many wizards undoubtedly having the inclination to work on it. If nothing like Hogwarts has been built over the course of the series, it is simply because there was no need. Have we lost the secrets of building pyramids? Would it be impossible to reproduce the Great Pyramid of Giza, or Schwedagon Pagoda, or El Tepozteco? No; styles and demand have moved on. In a world as small as magical Britain, demand for any new building is low, let alone another massive school. If nothing needs to be done, nothing will be done.

• The Hallows: This is trickier. The Hallows were, apparently, created by three extremely talented wizards. True, they undoubtedly kept their work secret, and perhaps made some unlikely discoveries. The Cloak, I suppose, one can pass off as disinterest. But why would no one attempt to produce another Stone, given that spells such as Priori Incantatem produce similar (albeit vastly inferior) effects? And after so many centuries, with magical research not really being stagnant, is it plausible that no one came up with a way of increasing the power of a wand? Especially since Gregorovitch actually was trying to replicate the properties of the Elder Wand, and actually had the wand itself? The best explanation I can think of is that the Hallows were indeed created by Death, or with said entity's assistance, and that Dumbledore is a big liar, which is self-evident. A more mundane possibility is that they were created with the aid of other magical creatures, a tactic which would have occurred to very few wizards.

• The Philosopher's Stone: This is the trickiest. Flamel survived into the modern period. He was well-known, and indeed worked on alchemy with Dumbledore. The Stone could be used by someone other than its creator, as evidenced by Voldemort's desire to possess it. Clearly, there is a tremendous demand for immortal life and abundant gold. And it was obviously beyond even Voldemort's abilities to produce one. Explanations are thin on the ground here, but the most plausible (neither supported nor contradicted by canon) is that some component was necessary for the creation of the Stone that simply no longer exists. Perhaps some magical creature has gone extinct. Perhaps Nicholas also had the assistance of Death, who seems to delight in giving people ways around death which never work out in the end.

Answer 3

I would posit one other possibility, though Jonah included it a bit in his answer as well. I would say one very big possibility is that methods of thinking have changed as well. This is something we can see in modern inventions as well too. Some of Leonardo da Vinci's inventions (can't name them off the top of my head right now) are simply not re-producable now, mostly because we are set in certain ways of thinking. Much like our current beliefs and thoughts in regards to physics limits what is possible to make, i.e. if we changed how we thought about what was possible and impossible, we could likely come up with crazy new tech.

Most of the inventions thought of or made to accommodate things like space travel, like computer innovations and GPS, Radar, etc. were all things thought previously impossible. Even take Einstein for example. E=MC2 was truly mind-blowing in terms of physics and science. Not something anyone thought of at the time. True, war is a major factor in the invention of most of these items, but methods of thought are a major factor.

In the Wizarding world, I would think it's not so much the particulars of the invention itself that stop it, or necessarily a lack of knowledge, but more that current generation wizards simply wouldn't think of it because it's thought to be impossible.

Answer 4

The wizarding world has had at least three major wars by the time Harry begins attending Hogwarts. The Wizard/goblins war, Dumbledore and his mate and Voldemort. A lot of wizarding families and their knowledge could have entirely be wiped out during such. Also there is the question of whether public libraries even exist in the wizarding world? Sure school libraries exist as do private family libraries. However the cost of purchasing every book of interested for witches and wizards who are not in school throughout their lives guarantees knowledge will be lost. Especially for those who struggle to purchase even their school text. The fact that the there is no shop or even that Hogwarts itself doesn't loan textbooks for the year for a lesser fee then purchasing a second hand version of the book explains a lot about why and how knowledge has been lost. Knowledge is power. Those in control of the wizarding world; the Ministry, Dumbledore and Voldemort's followers want control of that power. Censor what is and isn't know. Voldemort's name isn't printed, few even know his real name, his linage. The restricted section exist but is restricted elder year students, fifth year up still need passes. Hermione the smartest witch of her age doesn't know things Ron does simply because he grew up in the wizarding world. Ron (possibly like most witches and wizards) just assumed their muggle raised friends know and understand things they grow up with, only explain things when they come up. Wizards like the Malfoy family wouldn't even bother explaining