The Book of Five Rings is a text on kenjutsu and the martial arts in general, written by the samurai warrior Miyamoto Musashi circa 1645. It is considered a classic treatise on military strategy, much like Sun Tzu's The Art of War.
Musashi describes and advocates a two-sword style (nitōjutsu): that is, wielding both katana and wakizashi, contrary to the more traditional method of wielding the katana two-handed. However, he only explicitly describes wielding two swords in a section on fighting against many adversaries.
In the next link you can find a full translation of this book, I hope you enjoy it!
samuraiconsulting.ca/5rings/ 
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