I agree with this. This is why there is such a gap. But that type of destruction of knowledge was common back then. If it was foreign knowledge, discovers would take what was useful to them and claim it as their own, destroy the rest, and force the inhabitants to learn their history, language, and perspectives. It wasn't until later on as civilizations matured, that they understood the value of what was lost by destroying that knowledge. I would hope that the lesson has been learned but human history has shown that there will always be someone out there that makes it a goal to destroy knowledge. A nuclear war would have a similar effect. Things of great value would be lost that aren't related to money, jewels, and precious metal. All research, knowledge, and information within the area of destruction would vanish.