The first index was devised to let a busy ruler know what parts of a book he could skip. Later, indexes were used to provide snarky commentary (“Let no damned Tory index my history”). And throughout, just like with every new technology, people were afraid it would turn the youth into lazy, less serious citizens of the world. If any of this sounds interesting to you, I highly recommend Index, a History of the by Dennis Duncan. I will, however, suggest reading the book versus listening to the audiobook. Index entries do not always make for the most interesting listening.