It has survived to this day.

Ahmad al-Farghani (c. 800–870) was one of the most renowned astronomers of the 9th century, known in Europe as Alfraganus. He served as an astronomer at the Abbasid court and was also an engineer who supervised the construction of hydraulic structures.

Around 856, he wrote a treatise on the astrolabe in Cairo. The work provided a detailed explanation of the mathematical principles underlying the construction of this instrument, which was used to determine the positions of celestial bodies.

In 861, al-Farghani supervised the construction of a large Nilometer on Cairo’s Rawda Island, a structure designed to measure the water level of the Nile River. Since agricultural yields and taxes were planned according to the water level, the structure was of great importance to Egypt’s economy.

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