Medieval books were incredibly expensive. When placed in a public place, for example in a cathedral or public library, they were often chained to the lectern or bookshelf on which they were placed (as you can see in this blog about Zutphen’s chained library). It turned the book into a prisoner. The chain and the book-attachment are almost always clunky, the chains usually rattly. Reading a book like this was a challenging and particularly noisy affair! It was not exactly contributing to the silence that was to be obeyed in a library - that jail filled with noisy prisoners.
Pic: Bloomington, Indiana University, Lilly Library, Ricketts 193 (12th century, including likely its binding); the chain is post-medieval (more here).