From around 1300 to 1500, in concert with improved armour, innovative sword designs evolved more and more rapidly. The main transition was the lengthening of the grip, allowing two-handed use, and a longer blade. By 1400, this type of sword, at the time called "langes Schwert" (longsword) or "spadone", was common, and a number of 15th- and 16th-century "Fechtbücher" offering instructions on their use survive. Another variant was the specialized armour-piercing swords of the estoc type. The longsword became popular due to its extreme reach and its cutting and thrusting abilities.