Hello, according to historical records the library of alexandira burnt partially in 380 a.d. and on 2 other occasions after. reference : http://en.wikipedia.org/wiki/Library_of_Alexandria There are some controversies about the number of times it did actually burnt. In my opinion this is what caused most of the delays, something like 300,000 (some say 500,000) documents burned, they burned because most of the documents were scrolls. The second cause is religion, from 380 to 1500, well, nothing significant in western culture happened in terms of scientific discoveries or advances, for example in 1252 a papal bull stated that heretics should be tortured and killed. Remember that most of these people (men and women) were inventors, scholars or scientists, I have heard once a statistic saying that as much as 30,000 people died because of religion in those times. Many of them could have been Archimedes or Leonardo Da vinci. Simon Plouffe