What is Kakumune in Japanese Katana terminology?

The term "Kakumune" (角棟, かくむね) refers to a type of back ridge on a Japanese sword, which is characterized by its flat shape. It is also commonly known as "Hiramune" (平棟, ひらむね). This is the oldest style of back ridge found on Japanese swords, and it is often seen on swords from the Jokoto period (pre-987 AD). However, with the advent of curved blades in Japanese swords, this style of back ridge has become less common. The shape and style of the back ridge is an important aspect of a sword's design, contributing to its overall aesthetic and functional characteristics.