The world has never been more technologically advanced than it is now, but that doesn't mean that some things haven't been lost along the way.
Many of the technologies, inventions, and manufacturing processes of antiquity have simply disappeared with the passage of time, while others are still not fully understood by modern day scientists. Some have since been rediscovered (indoor plumbing, road building), but many of the more mysterious lost technologies have gone on to become the stuff of legend. Here are five famous examples.
1. Greek Fire
Perhaps the most famous of all lost technologies is what is known as Greek Fire, an incendiary weapon that was used by the military of the Byzantine Empire.
A primitive form of napalm, Greek Fire was a kind of "sticky fire" that would continue burning even in water. The Byzantines most famously used it during the 11th century, when it was credited with helping to repel two sieges of Constantinople by Arab invaders.
Greek Fire could be deployed in many different ways. In its earliest form it was poured into jars and thrown at enemies like a grenade or a Molotov cocktail. Later, giant bronze tubes were mounted on warships, and siphons were used spray the weapon at enemy vessels.
There was even a kind of portable siphon that could be operated by hand in the style of a modern flamethrower.
How was it lost?
The technology behind Greek Fire certainly isn't completely alien. After all, modern militaries have now been using similar weapons for years. Still, the closest counterpart to Greek Fire, napalm, wasn't perfected until the early 1940s, which would mean the technology was lost for several hundred years.
The weapon's use seems to disappear after the decline of the Byzantine Empire, but just why still isn't known.
Meanwhile, the possible chemical composition of Greek Fire has been widely studied by historians and scientists. An early theory was that the mixture included a heavy dose of saltpeter, which would make it chemically similar to gunpowder.
This idea has since been rejected, because saltpeter wouldn't burn in water. Instead, modern theories propose that the weapon was more likely a cocktail of petroleum and other chemicals, possibly including quicklime, niter, or sulfur.
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