The Library has rules.
Return your books on time.
Don't damage books.
Don't steal books.
Don't damage Library property.
Don't harm those within the Library.
You don't want to break the rules. If you do, you will be caught. Offenders are forced to serve the Library. Sometimes for a few years, sometimes for centuries. Until they have served out their sentences, they are trapped in strange, inhuman forms, the better to fulfill their new functions. They can all be identified by their dark brown robes. There are many different forms among these servants, but there are three that one is most likely to encounter.
These Librarians serve at the desks in the Main Hall of the Library. They have no eyes, but they know instinctively where to find any book in the Library. They also distribute the Library cards, check books out to people, and keep track of who has which book. If you look behind the desk, you'll find they have no legs, but instead are connected directly to the chairs that are rooted in the marble floor.
The most common of the Librarians, Docents guide people through the Library, showing them where to find books, as well as stalking the stacks for violations of the rules. They are perfectly silent, and in fact have no mouths. Where their left hand should be, a chain grows, connected to a brass lantern that never grows dim.
Pages reshelf the books in the Library. They have anywhere from six to ten arms, bowed legs, and squat bodies, making them excellent climbers, able to reach the highest shelves without need for a ladder. They rarely so much as touch the ground.