The Royal Library of Alexandria is estimated to have had over half a million documents and house about 100 scholars, according to [this article](http://ehistory.osu.edu/world/articles/ArticleView.cfm?AID=9). This would suggest a fairly decentralized archiving system, perhaps with every section having its own system of record keeping.

According to the relevant [Wikipedia entry](http://en.wikipedia.org/wiki/Library_of_Alexandria), the library also engaged in textual criticism, which implies further detailed record-keeping.

Apart from that I couldn't find any other insights into how the collection was organized. What do we know about the indexing system used by the Library? To clarify: the title refers to the organization of the manuscripts, not the structural organization of the Library itself.