in the 11th century, the monk theophilus described in his treatise, known as "schedula diversarum artium" ("list of various arts") or "de diversis artibus" ("on various arts"), all of the steps required for the construction of a church organ. the instrument described by theophilus was operated by a system of knobs and drones. air pressure was maintained by stepping on air-filled hoses positioned at the player's feet.