Here's a little article I wrote, way back when:
Sword Length Prohibitions The early regulations relating to the length of blades have been mentioned, several attempts were made at reducing the number of sword wearers, as will now be seen: In the second year of Kencho (1250), Hojo Tokiyori prohibited ordinary people from carrying long swords. This regulation was enforced by Akashi Kanetsuna, since then, common people and all priests carried long Kogatana called Wakizashi no Tachi. In Tensho XVI (1588), Hideyoshi made a proclamation to obtain from common people the surrender of their swords. Being a cunning man, he announced that it was his intention to build a Daibutsu Temple in Kyoto, and that he required thousands of nails, and he wished people to hand over their swords so that they might acquire merit towards a future life by stopping their earthly fights and contributing towards a religious cause. But people were less interested in a problematic paradise than in actually protecting themselves, and they did not rise to his bait. In Genna VIII, the Shogun Tokugawa Iyetada prohibited common people from wearing swords to avoid brawls; the Tachi was called then O Wakizashi. In Kwanyei XVII (1640), Tokugawa Iyemitsu prohibited the attendants of Bujin from carrying tachi. In Kwambun X (1670), Tokugawa Iyetsuna issued a regulation making the length of tachi 2'8"-9", and o-wakizashi 1'8", and anyone carrying a longer sword was liable to punishment. In Tenna III (1683), Tokugawa Tsunayoshi reiterated the prohibition to common people to wear the long sword, but allowed them to carry a tanto; musicians and painters, even when of the Samurai class, were debarred from carrying a big sword. In Kwansei X (1798), it was decided that any sword exceeding 1'8" should be termed Naga Wakizashi, and anyone carrying such a sword was liable to punishment. Later, the length was reduced to 1'5". Finally, in Meiji IX (1877), the Haitorei was issued prohibiting the wearing of swords, except the one sword belonging to soldiers and police when in uniform.