Banu Musa Brothers and the Book of Ingenious Devices

The Banu Musa (“sons of Musa”) were three brothers, Muhammad, Ahmad and al-Hasan, who worked in Abbasid Baghdad in the ninth century. Around 850 they produced the Kitab al-Hiyal, or Book of Ingenious Devices, the earliest surviving Arabic treatise on mechanical engineering, describing about a hundred automatic machines and trick vessels. They were also respected mathematicians and astronomers, and generous patrons of the translation movement that brought Greek science into Arabic.

Background: science in Abbasid Baghdad

In the early ninth century Baghdad was one of the largest cities in the world and the political centre of the Abbasid Caliphate. The caliph al-Ma’mun (r. 813–833) actively supported scholarship, sponsoring translations of Greek, Persian and Indian works and astronomical observations. The library and scholarly circle associated with him is known as the House of Wisdom.

Into this world came the sons of Musa ibn Shakir. Medieval biographers say Musa had been a highwayman in his youth in Khurasan before becoming an astronomer and a companion of al-Ma’mun. When he died, the caliph took his young sons under his protection and had them educated, apparently under the astronomer Yahya ibn Abi Mansur.

The three brothers

The exact birth dates of the brothers are unknown, but they were probably born around 800 or a little later.

• Muhammad (died 873), the eldest, was the leading geometer and astronomer and the most politically influential, serving several caliphs.
• Ahmad was the mechanic of the family and is usually credited with most of the Book of Ingenious Devices.
• Al-Hasan was known especially as a geometer; sources describe him as a gifted mathematician.

The brothers became rich and powerful. They spent large sums buying Greek manuscripts in Byzantine lands and paying translators. Muhammad is said to have met the young Thabit ibn Qurra in Harran and brought him to Baghdad, where Thabit became one of the greatest mathematicians and translators of the age. They also employed the famous translator Hunayn ibn Ishaq.

The Book of Ingenious Devices

The Kitab al-Hiyal was written around 850. In his 1979 English translation, the historian of technology Donald R. Hill numbered about a hundred devices. Most are trick vessels: jugs and basins that pour different liquids in turn, refill themselves, or dispense a fixed amount and then stop. Others include automatic fountains that change shape, a lamp that trims its own wick and adds oil, and a grab for recovering objects from water.

The brothers knew the pneumatic devices of Greek engineers such as Philo of Byzantium and Hero of Alexandria. But Hill and later historians stress that the Banu Musa went well beyond their models. They used small changes in air and water pressure, siphons, floats and conical valves to make devices that controlled themselves, an early form of what engineers now call automatic control.

Many devices were clearly meant to amuse and astonish courtly audiences. Their importance lies in the mechanical ideas behind them, which later engineers developed further. The best-known successor was al-Jazari, whose book of 1206 refers back to the Banu Musa.

The self-playing instrument

A separate short treatise attributed to the Banu Musa describes “the instrument that plays by itself”, an automatic flute player. Water power drove a rotating cylinder fitted with pins; the pins opened valves that sent air through the pipe and so played a tune.

Because the melody could be changed by changing the pins or the cylinder, some historians have called it one of the earliest known programmable machines. The principle of the pinned cylinder reappeared centuries later in European music boxes and barrel organs, though a direct line of influence is difficult to prove.

Mathematics and astronomy

The brothers’ most influential mathematical work was a book on measuring plane and spherical figures. Drawing on Archimedes, it dealt with the area of the circle, the volume of the sphere and the trisection of an angle. In the twelfth century Gerard of Cremona translated it into Latin as the Verba filiorum, also known as the “Book of the Three Brothers”, and it was used by European mathematicians such as Leonardo Fibonacci.

The brothers also made astronomical observations in Baghdad and Samarra over several decades, recording solar and lunar data. Several medieval writers link them to al-Ma’mun’s project to measure the length of one degree of the Earth’s meridian on the plain of Sinjar, though accounts of who took part differ.

Rivalries and engineering at court

The brothers were not only scholars but also courtiers with enemies. According to the later biographer Ibn Abi Usaybi’a, they intrigued against the philosopher al-Kindi under the caliph al-Mutawakkil and had his library confiscated. The same account says they were later embarrassed when a canal they supervised, dug by the astronomer al-Farghani, was badly levelled, and that the library was returned. The story cannot be independently confirmed.

Timeline

• 813–833: Reign of al-Ma’mun, patron of Musa ibn Shakir and his sons.
• c. 830s: The brothers are educated in Baghdad under caliphal protection.
• 847–861: Reign of al-Mutawakkil; the brothers are powerful at court in Samarra.
• c. 850: The Book of Ingenious Devices is written.
• 873: Death of Muhammad ibn Musa, the eldest brother.
• 12th century: Gerard of Cremona translates their geometry into Latin.
• 1206: Al-Jazari completes his book of mechanical devices, building on their tradition.
• 1979: Donald R. Hill publishes an English translation of the Kitab al-Hiyal.

Why it matters

The Banu Musa show how Abbasid scholars absorbed Greek science and pushed it further. Their self-regulating devices and pin-cylinder instrument are landmarks in the history of automation, and their patronage helped make Baghdad a centre of learning that later shaped European science.