Why do old libraries have chains?

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Tags

1. #library
2. #bookcase
3. #removed
4. #stolen
5. #shelves
6. #valuable
7. #which
8. #chain
9. #typically
10. #attached
11. #taken
12. #their
13. #chained
14. #allow
15. #itself
16. #being
17. #where
18. #purpose
19. #sufficiently
20. #books