Many of the books of science and humanities had been written prior to the founding of the Library of Alexandria and the Museion. From the frequency of use of the word "library" in Greek, it is probable that quantities of books were written, sold, collected, and critiqued at least since the fifth century BC.
During this period, many libraries, big and small, private and public, existed. What was new in the third century BC was the emergence of a category of scientists and researchers who were affiliated with the Library and were dedicated to its service.
The library became a gathering place for all the intellectuals of the sections of the Museion, for physicians needing the writings of Hippocrates and his followers, or for astronomers requiring a record of the weather conditions or knowledge about the early theories of astronomy. It was important for the scientists of the Museion to be aware of knowledge from the past.
However, that did not necessarily mean that these early records and papyri, such as Egyptian and Babylonian records of astronomical systems and weather conditions or ancient papyri dealing with astronomy and divination were part of the library's collection. Earlier scientific treatises were not that numerous and it was easy for scientists to possess a copy of them in their homes or laboratories.
The importance of the library increases for those interested in the humanities. The library not only provides general information, but also contains the great books of human thought. While the student of anatomy could find books on anatomy, the library could not provide him with bodies to dissect. The student of literature, on the other hand, could read the Iliad or the Odyssey or the songs of Anacreon or the poetry of Simonides.
These masterpieces might only be found in the library. The library may have been the mind of the Museion, but could also be considered the heart of the study of the humanities.