Most educated people know about the burning of the great library of Alexandria, and what a tragedy for humanity that was.
But I suspect that fewer people – at least in the Western hemisphere – know about the Quin dynasty’s massive campaign of book burning in 213 BC.
The emperor Qin Shi Huang (秦始皇), at the suggestion of his chancellor Li Si (李斯), instituted book burning (he condemned “all previously written historical books as worthless and ordered them burned, much to the detriment of our understanding of early Chinese history,” according to Jared Diamond), the persecution of intellectuals (including the burying alive of many Confucians), and a restriction on formal education for the common people. I think this can fairly be described as proto-totalitarianism.
As with the great library of Alexandria, we can only speculate about what has been lost.