From the late Heian period and the early Kamakura period (1185-1333) we can see the Japanese sword as we know it: shinogi-zukuri (ridgeline) construction, with a wide base, narrowing acutely towards the small point section (ko-kissaki). They are quite slender blades with the curvature concentrated between the handle and base. This shape is called koshi-zori. From midway towards the point there is very little curvature. These blades are usually around 2.5-6 shaku in length (75.8 cm-78.8 cm)
