Built in a.d. 715 to help measure the peak and trough of the Nile flood.
Nothing was built until the the 20th century to measure the extremes of the Nile flood.
mnli hypothesis: Nothing was built until the the 20th century to measure the extremes of the Nile flood. premise: Built in a.d. 715 to help measure the peak and trough of the Nile flood.