The destruction by fire of the great Library of Alexandria, begun in 48 BC by Julius Caesar when he was forced to set fire to his own fleet and the blaze spread to the docks and to the Library and completed by the Caliph Omar nearly seven centuries later in 642 AD during the first frenzied and seemingly irresistible flames of the Islamic Faith rampaged through the Arab world, was a severe setback for Western Civilization. The Library had contained about seven thousand scrolls written by Greek, Persian and Egyptian poets, writers and philosophers.
The Caliph Omar is said to have commented: If they are to be found in the Koran then they are not needed. If they are not to be found in the Koran then they are harmful.
How much of the fruit of that wise age was lost? Not all of the most powerful search-engines in the world can discover that because it became unknown or non-knowledge.