Societal knowledge

Of course human beings continue to learn more about the world: the ancient Greeks couldn't put a human being on the moon, the germ theory of disease wasn't fully accepted by doctors until, what, a  a century and a half ago?

But we also lose knowledge:
*archological sites give us new knowledge of human origins and the timing of human accomplishment. Bombs obliterate this, as was done in the first US Gulf War a quarter century ago, and more recently in Syria.
*the notion that everything is made up of atoms --which led eventually to the atomic bomb and plastics, amongst many other things--- was first proposed hundreds of years BC: but, by luck,  Democritus's writings were lost, and Plato's (among others) were preserved, all by accident. What if it had been the reverse? (From Charles Van Doren's _History of Knowledge_).
*I read, somewhere, in English, that there are languages that are only spoken by a few senior citizens, that once they die, the language may too.
* So-called primitive people sometimes know that an obscure plant will treat a particular symptom. Pharmaceutical companies investigate this, and it can be the origin of some new wonder drugs. If the peoples, or the plant, go extinct, so does that knowledge.
*The Pinkerton Detective Agency protected the President of the United States before the Secret Service did. The Pinkerton detectives were also involved in a vast array of issues, from labor strikes to investigating fake psychics. So is the burning of their records insignificant?
*Which isn't as bad as the case of the massive scale of records destruction in the Chinese cultural revolution. Historians of China are at a loss: the records of earlier times were systematically destroyed.
*Houdini was one of the highest paid entertainers of his era, and remains an icon 90 years after his death. Too bad he was buried with some of his family correspondence in his coffin.

Can you think of other examples of knowledge that was destroyed, permanently, by accident or on purpose?


(Note: Source: the concept of "lost knowledge" was introduced to me by Peter Burke's _Social History of Knowledge_. I don't know if he discusses any of my examples).