Scientific progress is rarely linear, but it’s fairly unusual for an invention to be created and then completely lost to time. A couple of often-touted examples include Stradivarius violins and Damascus steel—but neither of these actually qualify because, while the specific techniques once used to create them have been lost, they have effectively been recreated by modern luthiers and blacksmiths respectively. But there are a handful of lost inventions that modern science hasn’t been able to recreate (at least so far!)—here are five of them.

1. Girolamo Segato’s Petrification Method
2. Greek Fire
3. Roman Concrete
4. Zhang Heng’s Seismoscope
5. The Antikythera Mechanism

Girolamo Segato’s Petrification Method

Italian anatomist and naturalist Girolamo Segato took his first archaeological trip to Egypt in 1818, and five years later he had created his own preservation technique inspired by ancient Egyptian mummification. But instead of dehydrating corpses as the Egyptians did, Segato essentially petrified and mineralized them, thereby preserving the body’s original shape and color.

A surgeon from America, Valentine Mott, visited Segato and later wrote that the Italian’s petrification method left a cadaver “in a state of such stony hardness that it could be sawed into slabs and elegantly polished!” Segato was reluctant to share the secrets of his technique, though, and even destroyed all of his scientific notes after a few burglary attempts on his house.

When Segato died in 1836, all knowledge of his petrification process died with him. His tombstone in Florence’s Basilica of Santa Croce reads: “Here lies Girolamo Segato, his body hard as stone, if only his art hadn’t perished with him.”

Greek Fire

In the fantasy book and TV series Game of Thrones, there’s an incredibly dangerous incendiary weapon called wildfire that burns bright green and can’t be extinguished by water. Such a weapon might seem fantastical, but a real-world version did once exist (it just wasn’t a vibrant green color!)

Greek fire is believed to have been invented in 672 CE by Callinicus of Heliopolis. As in Game of Thrones, the recipe of the substance was a closely guarded state secret. Up until the 13th century, the Byzantine Empire made effective use of the weapon in war—particularly during battles at sea. Greek fire was either launched like grenades in pots or sprayed from tubes.

The exact ingredients of Greek fire remain unknown to this day, but it’s thought that petroleum was likely the base liquid. What else went into the flammable mix isn’t known, but historian John Haldon thinks that two of its other key components might have been naphtha, a very combustible crude oil, and pine resin, which would have helped the concoction burn hotter and for longer.

Roman Concrete

Concrete is one of the literal building blocks of human civilization, but the type of concrete that we use today is actually inferior in some ways to the kind that the Romans were using 2,000 years ago. While modern concrete erodes over time, ancient Roman concrete gets stronger—particularly when exposed to seawater.

“Contrary to the principles of modern cement-based concrete, the Romans created a rock-like concrete that thrives in open chemical exchange with seawater,” explained geologist and geophysicist Marie Jackson.

Although such a substance would be a boon to the building industry, there’s unfortunately no record of the exact recipe. Jackson is one of the scientists attempting to reverse engineer Roman concrete from existing structures.

The secret lies somewhere in the chemical reaction that occurs when the lime and volcanic ash in the concrete comes into contact with seawater. The resulting mineral growth serves to strengthen the concrete, and scientists are now mapping those minerals in an attempt to recreate the incredibly strong and durable substance.

Zhang Heng’s Seismoscope

Zhang (or Chang) Heng was an accomplished Chinese scientist and statesman who lived during the Han dynasty. He made important contributions across a variety of subjects, including mathematics, astronomy, and cartography, and in 132 CE he created the earliest known seismoscope—an earthquake-detection instrument. But exactly how Zhang’s device worked remains a mystery.

Replicas of Zhang’s seismoscope have been created from written descriptions. It looked like an urn and featured eight dragon heads around the outside, which aligned with the eight points of the compass. When the device detected the tremors of an earthquake, a ball would drop from a dragon’s mouth into the mouth of a frog below, thereby indicating the direction from which the shock waves came. But the internal mechanics of the seismoscope have been lost to time.

Many scientists believe that a pendulum system must have been used, but none of the modern recreations have been able to match the documented range and accuracy of Zhang’s original, which once reportedly detected an earthquake 400 miles away.

The Antikythera Mechanism

In 1901, a team of divers recovered a mysterious object about the size of a shoebox from an ancient Roman shipwreck just off the coast of Antikythera, a tiny island located between mainland Greece and the larger island of Crete. For decades, the wooden and bronze object was ignored in favor of other treasures found on the shipwreck, but when researchers finally turned their attention to it in the 1970s, they discovered that it was a mechanical marvel.

Often described as the world’s first analog computer, the Antikythera Mechanism showcases technology that researchers didn’t previously believe existed during the classical period. In fact, similar technology doesn’t even crop up again for more than 1,000 years. 

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