10 Times Humanity Found the Answer (and Then Forgot)

In the ancient world, the ultimate expression of fire as a weapon of terror and ruin was a near-unquenchable "napalm" called Greek fire — a substance so legendary in its effects that "Game of Thrones" used a fictional version to decisive effect in its own epic (though fictional) Battle of the Blackwater.

In truth, the term "Greek fire" pops up all through history to describe several ancient and medieval substances combining various elements. Early versions used pitch, naphtha or sulfur, while Crusaders later faced Greek fire made with saltpeter and turpentine.

But for the real deal, scholars focus on a certain event that took place in seventh-century Constantinople (that's modern Istanbul, in case you don't know the They Might Be Giants song). There, in the year 673, true Greek fire — petroleum-based, self-lighting and impervious to water quenching — was said to have been used to devastating effect by Byzantine emperor Constantine IV's forces against an attacking Arab fleet. Sources claim the Greek ships launched the fire in pots or spat from tubes, possibly powered by Roman pumps [sources: Beschizza, Encyclopedia Britannica, National Geographic Channel].

Some have argued that the true Greek fire, invented by Callinicus of Heliopolis, a Jewish refugee from Syria, was already lost by then, and that the Constantinople formula was a weak imitation [source: Beschizza]. Oh, well — that's the problem with taking state secrets to your grave. Although we think we know Greek fire's basic fixings, the method of putting the stuff together remains a mystery — a reminder that, as with chemistry and baking, knowing the recipe is not always enough [sources: Encyclopedia Britannica, National Geographic Channel].

In the Tom Stoppard play "Rosencrantz and Guildenstern Are Dead," dimwitted Rosencrantz repeatedly stumbles onto notable scientific and technical discoveries, often via toys (neither he nor Guildenstern grasp what he's done). These droll scenes raise a thorny question: Do you have to recognize a thing's operational principle to lay claim to discovering it? Should we credit the inventor of a steam-driven toy with the discovery of steam power?

Whatever your answer, there's no question that the aeolipile, a toy devised in the first century by inventor Heron of Alexandria, was a steam turbine — a device that turns the thermal energy of escaping steam into mechanical energy. As far as we know, Heron's device — a water-fed sphere, mounted on its axis above a heat source, that spun thanks to steam escaping from two bent tubes sticking out from its middle —never attained more than amusement status. But the idea that inventors would begin to re-examine in the 17th century, and that would drive the Industrial Revolution during the late 18th and early 19th centuries, was there — regardless of whether anyone in Heron's time grasped why it worked [sources: Encyclopedia Britannica, Martin, Palermo].

Interestingly, Heron himself collected ancient knowledge, so as some of his works were lost — some briefly, some forever — so too were stockpiles of ancient Babylonian, Egyptian, Greek, and Roman math and engineering progress [source: Encyclopedia Britannica].

Heron was not alone taking delight in vaporous water. A Greek living in Egypt, he was part of the first-century Roman Empire, and the Romans knew their way around steam. For one thing, they used steam in their public baths — facilities so central to Roman society that some saw the bath as the symbol of Rome itself (the Baths of Caracalla covered more area than St. Paul's Cathedral and could handle 1,600 people at a go) [source: Suddath].

No mere watery tubs, various bath complexes featured outdoor sports areas, food stands, servants, dressing rooms, cold rooms, warm rooms and, of course, a steamy Caldarium. Making this sauna-like room possible was an innovative technology called the hypocaust — which also happened to be one of the first examples of indirect heat [source: PBS].

For most of human history (and prehistory), we were stuck with direct heat from fires, hearths and, later, stoves. Today, our homes use indirect heat, in which heat energy from a central source flows through the house via air, steam or water.

The Romans' hypocaust involved a brute-force version, which channeled fire-heated steam through passages beneath floors and inside walls, but it worked [source: PBS]. After Rome's collapse, Europe mostly returned to its pits and hearths for heat. Central heating would not re-enter the Western world in earnest until the late 18th and early 19th centuries, driven in part by the advances of the Industrial Revolution but slowed by ventilation issues, fire and explosion risks, arguments between architects and engineers, and the need to convince homeowners to convert from tried-and-true heating methods [source: Bruegmann].

Through their baths and other plumbing advances, the Romans spread hygiene throughout their empire — although, as we'll see in the next section, not as effectively as they might have hoped.

Joining the Roman Empire, even at the point of a sword, brought with it certain perks. No question, the Romans were groundbreaking engineers, and they often turned that genius to the art of moving, storing and utilizing water. Via aqueducts, underground passages and cisterns, they conveyed water over vast distances, watered fields, fed fountains and, in a sense, flushed their toilets.

When not using the loo at home, Romans did their business using large public latrines, in full view of one another. Within them, beneath rows of marble thrones, channels of running water swept waste into the sewers. But because the Romans lacked both toilet paper and a theory of bacteria, all was not flush with success. In fact, Roman latrines and baths retain signs of many of the diseases and parasites that their hygiene methods ought to have washed away. One explanation: After "bombing at the forum," the Romans passed around a shared sponge on a stick to clean their "Appian Way" — not the most hygienic option. But it's also likely that they didn't change their baths' water often enough, and that the night soil (human poop) with which they fertilized their crops might have brought parasites back in via the food supply [sources: Beck, Smithsonian, Suddath, Wenz].

The Romans didn't invent plumbing, nor did it disappear when Rome fell. Rather, through them it reached an apex to which, after Rome's fall, Europe would not draw near for another millennium [source: Suddath].

It's an old story: You're hanging out with your blacksmith, metallurgist and weapon-enthusiast friends and you've run out of things to argue about. Sure enough, someone brings up the legendary metal weapons once traded in medieval Damascus, famed for their supposedly irreproducible strength, edge and wave pattern. One friend hammers on about how "damascened" steel is no lost secret metal or technique, but merely a method of billet welding, in which different metals are fused, drawn and folded to create a wave pattern. Another defends to the hilt the view that these fabled blades were truly unique.

So who's right? Well, although we can make blades today that rival Damascus steel weapons, few would dispute that their plasticity, strength and keen edge were amazing for their day. Nor has anyone yet made blades with quite the same characteristics as the originals, even when starting with the same carbonized steel that the weapon masters of Damascus likely used [sources: Verhoeven et al., Wadsworth and Sherby].

The method for making Damascus steel blades was a closely guarded secret, like much of the armorer's art, and was lost when trade in the blades failed in the late 18th century. One theory holds that the art died when its source of iron in southern India, which perhaps produced ore peppered with key impurities like tungsten and vanadium, tapped out. Blacksmiths' legendary quenching liquids, rumored to range from urine to the bodies of slaves, long provided another possible explanation for the weapons' strength and edge-holding qualities. Today's theories, however, favor lost techniques of thermal cycling or low-temperature metalworking [sources: Sullivan, Verhoeven et al., Wadsworth and Sherby].

Either way, you can have damascened steel, but Damascus steel blades may well be unique items, like Stradivarius violins. And no one will ever crack that mystery ... right?

Does it change our view of a lost art when we've learned the trick to how it was done? If we could, as is suggested in the film "Head Office," mass-produce violins that look, sound and smell like Stradivari's famed instruments, would we stop valuing the originals?

We doubt it. In fact, understanding, as we now do, how Antonio Stradivari brought the violin to its highest form at the turn of the 18th century only elevates our respect for the feat. For Stradivari's contributions extend far beyond the unusual woods or special varnishes to which many credited his instruments' stellar sound; they encompass the evolution of the violin itself. Stradivari helped to work out the violin's ideal shape and size, from designing a new bridge to stretching the body and making it shallower [sources: Encyclopedia Britannica, Encyclopedia Smithsonian].

It's true that the secrets of Stradivari's shop in Cremona, Italy — which also made cellos, guitars, harps and violas — have been lost for more than 250 years and that modern scholars have yet to discover the secret of his varnish [sources: Encyclopedia Britannica, Encyclopedia Smithsonian]. But it's also true that experts no longer consider the chemicals in the varnish — intended to protect the wood from worms — to be the solo contender for explaining the violins' evocative sound. Modern analysis suggests a blend of first-chair contenders, including a careful ratio of material thicknesses in the top and back plates, the arrangement of tiny pores in the wood and some as-yet unidentified chemical treatments [sources: Conner, RSNA, Texas A&M University].

It's been said that there's a fine line between folk remedy and medicine, but we would argue that the line is in fact quite wide, and it's defined by a simple question: What can be scientifically proven to work? Unfortunately, that proof can take centuries, even millennia, to move beyond mere anecdote. Hippocrates advised pain and swelling sufferers in the fifth century BCE to chew willow bark, but it wasn't until fairly recently that we learned not only that it worked, but why — namely, that white willow contains salicin, a close chemical cousin to aspirin (acetylsalicylic acid) [source: Ehrlich].

Fast forward to 2015, when an old English recipe for an eye salve began making news for its promise as a weapon against methicillin-resistant Staphylococcus aureus, aka MRSA, the obstinate scourge of hospitals and nursing homes. The brew, which contains garlic, onion or leeks, wine and cow bile, was described 1,000 years ago in "Bald's Leechbook," an Anglo-Saxon collection of remedies now housed in the British Library. Remarkably, when researchers concocted the remedy, it not only affected MRSA — it eradicated it [sources: BBC, Rayner].

Some scholars believe that the early physicians who contributed to the book used a proto-scientific trial-and-error method and kept careful notes on which mixtures worked and which ones failed. Unfortunately, the MRSA killer had to spend a millennium forgotten among dubious tonics before its value was found again [sources: BBC, Rayner].

In a sense, this technology was lost twice: First, when the ship that carried it sank two millennia ago and, second, when historians, unmoved by hard-to-read X-rays of the day, left it to languish for more than a century after it was brought back to the surface in 1900-1901.

It was worth the wait. Once scholars sussed out what this laptop-sized object was — a gear-based machine for correctly modelling the movement of the planets, moon and sun — it changed the way we thought of Greek gear technology, to say nothing of the precision of mathematical calculation the device implied. It's all there in the gears: For example, one gear's 235 teeth match the number of months in 19 solar years (the shortest time in which solar and lunar cycles line up). The inventor might have inherited this idea from the ancient Mesopotamians, who used the 235-month cycle and built up great tables that tracked the sky's movements with remarkable accuracy. Other gears and ratios tracked lunar motion, even taking into account hitches caused by the moon's elliptical orbit [sources: Marchant, PBS, University of Puget Sound].

Since the decipherment of the so-called Antikythera Mechanism, some have quibbled over whether a planetarium qualifies as a computer, but it performs calculations that reveal when eclipses will occur, down to the hour — decades in advance. Lunar cycles were vital to the Greeks, who relied on them to cycle farming practices, time religious festivals, schedule payments and plot tactical advantages [sources: Marchant, PBS, University of Puget Sound].

Europe would have to wait until 1642 before an effective, geared mechanical calculator, the Pascaline, would be invented by French mathematician, inventor and philosopher Blaise Pascal. Cousin devices to the Antikythera Mechanism may have cropped up here and there in the medieval world, but true astronomical clocks would not reappear in Europe until the 14th century [source: Marchant].

Practically speaking, you can accomplish a surprising amount using only geometry, basic mathematics and a few choice rules of thumb. Eventually, though, the need to calculate trickier matters — rates of change, curvatures, areas under curves — demands that you develop mathematics that can handle them. This is where calculus comes in.

Today, we credit its development to both Isaac Newton and Gottfried Wilhelm Leibniz, both of whom developed it independently around the turn of the 18th century, but in truth the world's intellects had been flirting with the idea for millennia. Let's start by returning briefly to the ancient Greeks. In their mathematical heyday, they produced Eudoxus (c. 408-355 BC), whose method of exhaustion edged right up to the notion of the limit, and Archimedes (c. 287-212 BC), who came up with practical methods of calculation that bore a family resemblance to integral calculus. Exhaustion would later spring from the mind of fifth-century Chinese mathematician Liu Hui, too, and similarly significant strides were taken among medieval Indian thinkers [sources: Boyer, SLU]

These forerunners to calculus, like so many advances from antiquity that were lost with the fall of Rome, hint at the knowledge that was lost to Europe when it entered the Dark Ages. But as ideas, they also went begging in their own time because their potential was never fully realized [sources: Boyer, SLU].

The first people to discover the New World did not then lose it — they stuck around for the yummy mammoth meat they'd followed across the Bering land bridge. But depending on which research you read (and believe), you might be shocked by the roster of visitors who allegedly came and went afterward.

Every schoolchild knows the tale of the Norse explorers who sailed to Greenland and Iceland at the turn of the 11th century. Speculation that such sailors made it to Newfoundland during that century is borne out by the remains of the L'Anse aux Meadows settlement and the tales of both Vikings and indigenous peoples.

But Columbus's line of precursors didn't end with a Norse expedition from Greenland, at least not if you believe some (admittedly shaky) hypotheses. According to one well-known (and largely debunked) book, Chinese sailors beat Columbus to the New World by 71 years [source: Finlay]. Turkish President Recep Tayyip Erdogan has given voice to the fringe view that Muslims contacted Latin American civilizations three centuries before the Italian explorer first set sail [source: Tharoor].

A bit more mainstream are those who argue that Polynesians might have reached South America before any European stepped foot in the Americas. Although some potential proof of the hypothesis has been dealt a few blows of late, the Polynesians were prodigious sailors and settlers; when compared to their other deeds, such a feat certainly does not seem beyond their abilities [source: Smith].

Whatever the case, we know at least one group after the Bering Strait migrants found the Americas long before Columbus and didn't stick around for long. The New World might seem like a rather large thing to forget (actually, they recorded the discovery in their sagas), but the Vikings likely received some encouragement on their way out — from the fierce descendants of the first migrants [source: Parks Canada].