One of the problems pervading the study of medieval Islamic technology is the lack of surviving technical treatises. Tradition tended to be handed down by example and by word of mouth, and apprenticeships could last for decades. Fortunately, however, occasional treatises do exist. The treatise "On swords and their kinds" was written by the 9th century Muslim philosopher Ya'qub ibn Ishaq al-Kindi. This work was commissioned by a powerful patron of scholarship, the Abbasid caliph Mu'tasim, and the content of the treatise presumably reflects the ruler's general interest in his army and its...