How about Nalanda, India? The library was destroyed in 1197 - 1203 during the Muslim invasion in which Bakhtiyar Khalji sacked it and set it to flames.
The library alone was so vast that it is reported to have burned for three months after the invaders set fire to it, ransacked and destroyed the monasteries and killed or drove the monks from the site.
Unmolested? your definition must be pretty rough.
Feel free to add to the list I'm tempted to put Roman North Africa on the list but I do not know if Roman North Africa was a great civilization on it own.
From Wiki
"In 642 AD, Alexandria was captured by the Muslim army of Amr ibn al `Aas. There are five Arabic sources, all at least 500 years after the supposed events, which mention the fate of the library."
"Abd'l Latif of Baghdad (1162–1231) states that the library of Alexandria was destroyed by Amr, by the order of the Caliph Omar.
Yes the library had burn before but it was restored after acciendal fires. However when Islam destroyed it they destoryed it completely and never restored it.
Again from Wiki
"Omar replies: "If those books are in agreement with the Quran, we have no need of them; and if these are opposed to the Quran, destroy them."
As of 732, the date of the Battle of Tours. I was quarreling with the assertion that Charles Martel’s victory represented the “highwater mark” of Islamic expansionism.
Every place I listed was deliberately chosen because later Islamic expansionism washed over them, often with devastating results.