It is hard to determine precisely when the first "bokken" appeared due to secrecy in ancient martial arts training and loose record-keeping. While various mock weapons were surely used during the earlier periods of Japanese history, usage of a "bokken" in their modern form first emerged during the Muromachi Period (1336–1600) for the training of samurai warriors in the various ryūs (schools of martial arts and swordsmanship) of the era. If a malleable steel katana is repeatedly used, it can easily become nicked and the edge flawed, eventually leading to a broken expensive sword. "Bokken" are safer than fighting with real swords, and are considerably more durable; a wielder can make contact with other trainee's swords with little fear of damage.