The earliest form of the "bō", a staff, has been used throughout Asia since the beginning of recorded history. These were hard to make and were often unreliable. These were also extremely heavy. The konsaibo was a very distant variant of the kanabo. They were made from wood studded with iron. These were still too cumbersome for actual combat, so they were later replaced by unmodified hardwood staffs. Used for self-defense by monks or commoners, the staff was an integral part of the Tenshin Shōden Katori Shintō-ryū, one of the martial arts’ oldest surviving styles. The staff evolved into the "bō" with the foundation of kobudō, a martial art using weapons, which emerged in Okinawa in the early 17th century.