The Book of Ingenious Devices (Arabic: كتاب الحيل Kitab al-Hiyal, Persian: كتاب ترفندها Ketab tarfandha, literally: "The Book of Tricks") is a large illustrated work on mechanical devices, including automata, published in 850 by the three brothers of Persian descent, known as the Banu Musa (Ahmad, Muhammad and Hasan bin Musa ibn Shakir) working at the House of Wisdom (Bayt al-Hikma) in Baghdad, Iraq, under the Abbasid Caliphate. The book described about one hundred devices and how to use them. Overview The book was commissioned by the Abbasid Caliph of Baghdad, also made by Al-Jazari, Abu Jafar al-Ma'mun ibn Harun (786–833), who instructed the Banu Musa to acquire all of the Hellenistic texts that had been preserved by monasteries and by scholars during the decline and fall of Roman civilization. The Banū Mūsā brothers invented a number of automata (automatic machines) and mechanical devices, and they described a hundred such devices in their Book of Ingenious Devices. Some of the devices described in the Book of Ingenious Devices were inspired by the works of Hero of Alexandria and Philo of Byzantium, as well as ancient Persian, Chinese and Indian engineering. Many of the other devices described in the book, however, were original inventions by the Banu Musa brothers. While they took Greek works as a starting point, the Banu Musa went "well beyond anything achieved by Hero or Philo." Their preoccupation with automatic controls distinguishes them from their Greek predecessors, including the Banu Musa's "use of self-operating valves, timing devices, delay systems and other concepts of great ingenuity." Many of their innovations involved subtle combinations of pneumatics and aerostatics. The closest modern parallel to their work lies in control engineering and pneumatic instrumentation. In turn, the Banu Musa's work was later cited as an influence on the work of Al-Jazari, who produced a similarly titled book in 1206. Given that the Book of Ingenious Devices was widely circulated across the Muslim world, some of its ideas may have also reached Europe through Islamic Spain, such as the use of automatic controls in later European machines or the use of conical valves in the work of Leonardo da Vinci. Mechanisms and components Automatic controls The Banu Musa brothers described a number of early automatic controls. Two-step level controls for fluids, an early form of discontinuous variable structure controls, were developed by the Banu Musa brothers. They also described an early feedback