As time passed, the "spatha" evolved into the arming sword, a weapon with a notable cruciform hilt common among knights in the Medieval Age. Some time after this evolution, the earliest known treatises "(Fechtbücher") were written, dealing primarily with arming sword and buckler combat. Among these examples is the I.33, the earliest known "Fechtbuch". The German school of swordsmanship can trace itself most closely to Johannes Liechtenauer and his students, who later became the German masters of the 15th century, including Sigmund Ringeck, Hans Talhoffer, Peter von Danzig and Paulus Kal. It is possible that the Italian fencing treatise Flos Duellatorum, written by the Italian swordmaster Fiore dei Liberi around 1410, has ties to the German school. During this period of time, the longsword grew out of the arming sword, eventually resulting in a blade comfortably wielded in both hands at once. Armour technology also evolved, leading to the advent of plate armour, and thus swordsmanship was further pressed to meet the demands of killing a very well protected enemy.