There’s a Real-Life Inspiration for Game of Thrones’ Valyrian Steel. Here’s How Its Long-Lost Secrets Were Revealed

Warning: This post contains spoilers for Game of Thrones.

As the Game of Thrones saga winds down, Valyrian steel has never been more important. It’s one of the few substances known to kill White Walkers, but only about a half-dozen known characters currently wield weapons made from the magical material — and it’s not possible to make more. That’s because, according to the lore of the show and A Song of Ice and Fire books, the secret for forging the metal was lost long before the Game of Thrones story starts.

Valyrian steel is also one more way in which Game of Thrones, fantastical though it is, has links to real history. George R.R. Martin himself has told fans that Valyrian steel’s “closest real life analog is Damascus steel,” which is similarly renowned for its sharpness and strength. Valyrian steel also has a signature pattern that Martin describes as seeming to “ripple and dance down the dark metal.” Real-life ancient writers described Damascus steel’s “wavy marks like the tracks of ants.”

And, like the secret of Valyrian steel, the art and science of making Damascus steel was lost for hundreds of years.

Then, in 1981, the New York Times reported on the front page of the science section that Stanford University researchers appeared to have “stumbled on the secret of Damascus steel” after the “formula had been lost for generations.” Those researchers were Oleg D. Sherby and Jeffrey Wadsworth.

“Nobody knew how they were made and it was a well-kept secret,” Wadsworth, who has now retired as CEO of the private science development company Battelle, tells TIME. “We believe we succeeded.” (Sherby died in 2015.)

So what exactly is Damascus steel?

“The steels often came from India and they were forged in the Middle East and then sold in Damascus,” Wadsworth explains. “This had gone on for centuries. The steels were famous because they were tough and sharp and strong and better than competing steel swords — they’d defeat them in a contest, they’d break them, they wouldn’t themselves be fractured — and they had this unusual surface pattern. The surface pattern has many descriptors; they’re very elegant, some of them, like sands moving across the desert or like waves on the surface of water.”

European warriors broadly learned about Damascus steel through contact with Middle Eastern fighters during the Crusades in the 11th century, and were impressed by their sharpness, elasticity and hardness, as well as the patterned look of the blades, which could not be damaged even by the worst wear and tear. In his 1825 Crusades novel The Talisman, Sir Walter Scott describes an encounter between Saladin and King Richard, in which the Sultan impresses the English king by showing off the sharp edge of his scimitar, which was “marked with ten millions of meandering lines.” (This same moment is ripped off in a seduction scene in The Bodyguard, Wadsworth notes.)

How the blades got that way was a tightly held trade secret. Legends surrounded the question — from the idea that the metal was first fed to chickens and then essentially harvested from their droppings, to the idea that it was cooled after heating using goat urine or by “plunging it through the body of a muscular, active slave, so the slave’s strength would be infused into the metal,” as The Encyclopedia of the Sword puts it.

But as swords became less and less important to warfare, the Times reported in 1981, the methods of making this special steel were lost. For centuries, scientists and blacksmiths tried to figure out how the original had been made, but the secret of the steel seemed uncrackable.

Adding to the confusion was the fact that it was possible to replicate a sort of ripple pattern using a different method: laminating or pattern welding. In that technique, different types of steel are folded and layered to create the finished product. This technique also has ancient origins — and a Game of Thrones connection, with a Valyrian steel sword described as bearing ripples that are “the mark of steel that has been folded back on itself thousands of times” in A Storm of Swords. Over the years, the product of that technique came also to be called Damascus steel by many. However, though the ripples were there, this was not the same as the original Damascus steel, in which the pattern came from within, a result of the arrangement of the crystals in the material, a special kind of metal that was known as wootz, says Wadsworth.

“If you watch [the History channel show] Forged in Fire, when they talk about Damascus patterns, they’re invariably talking about layered metals,” he says. “But in fact the famous scimitars and swords from Persia were made the other way, which is much harder to do.”

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Sherby and Wadsworth came to their discovery by accident. At the time, scientists were racing to make advances in something called “superplasticity” — that is, trying to make metal alloys that became unusually stretchy at high temperatures. For steel, which is essentially an alloy of iron and carbon, this was difficult. Metallurgists knew they needed to get the grains in the steel smaller in order to achieve superplasticity, but that meant having more carbon than usual in the mix. However, once steel gets above 1% carbon, it’s more brittle at room temperature, and thus not as useful. However, it turned out that, by processing the steel with the goal of making it have that elastic quality (so, focusing on the tiny grain size), Sherby and Wadsworth ended up with a steel that was not brittle even though it had high carbon.

“It was at a conference we were at that somebody came up to us and said, ‘Hey, I think those steel compositions you’re using are identical to those in the famed Damascus steels,'” Wadsworth recalls. “I had heard of them but I had no idea of the linkage. So we started investigating Damascus steels.”

After comparing their work to ancient arms, Sherby and Wadsworth started working on achieving the signature ripple patterns on their steel, and realized they had made an important Damascus discovery: Though they still didn’t know precisely how ancient swordsmiths had done their work, they appeared to have figured out, on a chemical and physical level, part of what made Damascus steel special. In the years that followed, Sherby and Wadsworth encountered some push-back from others who had other theories about the centuries-long search for Damascus steel — research that has continued — but Wadsworth believes that their steel corresponds to that of ancient legend, thus solving a mystery that was lost for centuries.

And as it turns out, the reason why the technique was lost also has echoes in Game of Thrones.

In order to achieve Damascus steel, the artisans working on the metal would have had to be very specific about forging, heating, quenching (cooling) and tempering (reheating) the steel. But, without modern instruments, they couldn’t have known much about the chemical composition of steel and the precise temperatures for processing it.

“When you have a product that’s really good and you don’t know what you’re doing or how you did it, a lot of ritual becomes attached to it. By ritual, you repeat what you did,” Wadsworth explains. “That leads to a lot of theories about these swords being quenched into [the bodies of] slaves, to transfer the strength of the slaves to the sword. All these myths arise when you don’t really know what’s going on but you need to remember the time it worked.”

Helmut Nickel, then the curator of Arms and Armor at the Metropolitan Museum of Art, told the Times in 1981 that “legend had it that the best blades were quenched in ‘dragon blood.'”

That legend has its own Game of Thrones echoes: Lightbringer, the sword of Azor Ahai, the legendary hero whose reincarnation as the Prince Who Was Promised remains a major key to the future of the Thrones story. Though Lightbringer is not among the known Valyrian blades, Azor Ahai famously struggled with swords that were too brittle before succeeding at forging that sword by plunging the still-hot steel through the heart of his beloved wife, Nissa Nissa, so that, per A Clash of Kings, “her blood and her soul and her strength and her courage all went into the steel.”

Wadsworth says it doesn’t make any sense to believe that real Damascus steel was ever actually quenched by killing. Though it was sometimes have speculated that the human body could have been a source of carbon for the metal, he says evidence is lacking that it ever actually happened, and besides that, “a human body would be a very poor quenching medium compared to oil.”

That fact may be little consolation to those fans who worry that Lightbringer’s gory origin story might prompt a Jon or Daenerys to try to recapture the magic, as the fantasy realm doesn’t always take its cues from real life. After all, while real Damascus steel may no longer be a metallurgical mystery, the creation of Valyrian steel remains a lost secret to those who forge the swords of Westeros.