Yes there is lost technology, but it also depends on how you define “technology”. At one point, the lever and the wheel were cutting edge technology but as everyone knows, today’s cutting edge technology is tomorrow’s blunt instrument.
Significant one is Antikythera. This is the Antikythera Mechanism found in an ancient Greek shipwreck. Kind of looks like a clock. After decades of research we know now that it’s an astronomical device that calculates the position of the planets against a calendar, possibly to assist in worship of the Gods. Before finding this we had no conception that the ancient Greeks had the ability to fabricate screws, gears, bearings and surfaces that would calculate mechanically. This is very much like an old computer.
Uhlbert, a medieval sword made of stainless steel hundreds of years before the method for forming steel was known.
There are over 170 of this type of sword known to exist in Northern Europe. The shape, weight and design of this sword would have made it a super weapon of its time. Because it was made of steel it resisted rust, kept an edge, had a fine balance and a sharp, strong point that wouldn’t break off when piercing chain mail. Although scientists have worked out the methods by which it COULD have been made, it required such a leap of knowledge and experience by the metalsmiths of the time that it represented something unprecedented and that would not be rediscovered again until 400 years later.
Pozzolana, which today we call “Portland Cement”. This technology cannot be underestimated.
This substance allowed the Roman Empire to sprint far beyond every other empire of the time. It was a strong, hydraulic cement that resisted cracking and held up over time, so much time, in fact that many Roman structures still exist today and some are even in use. Roman aqueducts were built with pozzolana and sheep’s blood because it was discovered that it could withstand freezing weather better. When the Roman Empire fell, the knowledge of cement was lost. The enormous and strong structures of Rome were no longer capable and while there were many beautiful buildings built after Rome, none of them came close to the scope, strength and longevity of the Roman structures. “We stand on the shoulders of giants,” later scientists and philosophers would lament when speaking about the loss of Roman technology and abilities. Cement would not be discovered again until the late 1700s when someone in Maine discovered that certain ingredients mixed with lime and carbonate would create a chemical reaction in water that resulted in stone-like substance that could be formed into a method for adhering blocks or making huge slabs. This happened in Maine and is why the common name for cement is often “Portland”.
Trepanning is the practice of drilling or chiseling a hole into the skull. This was done to relieve swelling from a concussion. Or when combined with rudimentary brain surgery, it could “release the evil spirits” that caused seizures or migraines. Trepanation is an ancient practice, used by native peoples all over the world and dates back to Neolithic times. It may not even qualify as a “lost technology” since it’s still practiced today.
There are many unexplained technologies, from the Baghdad Battery, which was probably an electrolysis device, to the method for chipping, moving and building stone structures in Machu Picchu, to the ball bearing techniques used to move the massive stones of Stonehenge. Humans are ingenious. One might even say the Semmelweiss’ technology of hand-washing use of carbolics to raise the survival rate of new mothers and babies to the 90 percent level at the filthy hospitals of the time, before the knowledge of Germ Theory was a lost technology for he was given no credit and laughed out of medicine for even suggesting that it was possible to reduce infection through hygiene. It wouldn’t be until thirty years later that Lister and Pasteur came up with new protocols that proved germs were the cause of infection, leading to hair nets, and gloves and gowns and autoclaves for sterilizing instruments.
Anything that moves civilization forward is a technology no matter how simple it is to us today. The inclined plane made work easier but the ancient scientist who discovered that you could use the principle to make a “screw” that allowed the securing of two pieces of wood, or scaled up, to move water from wells, changed the world.