Nilometer
What the experts agree on
This 8th-century well measured the Nile's annual flood levels to predict harvests—guiding Egyptian farmers from pharaonic times until the Aswan Dam's completion in the 1950s.
“An ancient instrument used to measure the waters of the Nile so Egyptian farmers would know whether to expect famine or flood. ”
– Atlas Obscura
"Used from pharaonic times until the completion of the Aswan Dam in the late 1950s to measure the height of the flood." Full review
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"The Nilometre (Al-Miqyas in Arabic) dates from the 8C and was refitted in the 11C." Full review
"This well was used to measure the height of the Nile through the course of its annual fluctuations." Full review