This is a girdle book.

They made these in the middle ages so that you could take a book with you and read it while on a trip. They didn't have pockets so they made it so that it could be hung from your belt.

This is a page with pictures of real ones and a pattern that I found  to create your own cover that can hold  your own book.

This is a nice one.

Notice that it is upside down when you hang it on your belt. that way you can pick it up and read right away and still not have to remove it and have the fear of dropping the book in the mud while you are riding on the back of your donkey.

This one is so thick! 

This one is so small, but you don't realize it. 

This photo shows how small this one is.  

It's smaller than a paperback.

Here is another one.

I also like how the locks keep it shut.

The pattern below and the link are both the creation of Jaysen Ollerenshaw.