Thin tachi and chokutō-style blades were often unable to cut through the boiled leather armour of the Mongols, with the blades often chipping or breaking off.[13] The evolution of the tachi into what would become the katana seems to have continued during the early Muromachi period (1337 to 1573). Starting around the year 1400, long swords signed with the katana-style mei were made. This was in response to samurai wearing their tachi in what is now called "katana style" (cutting edge up).