Another Abbasid construction, the Nilometer on Rhoda Island, is the oldest original structure in Cairo, built in 862 AD . It was designed to measure the level of the Nile, which was important for agricultural and administrative purposes.
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Information recorded in the Royal Annals ( as preserved on the Palermo Stone ) includes measurements of the height of the annual Nile flood ( see Nilometer ), the Inundation, details of festivals ( such as Sed festivals ), taxation, sculpture, buildings, and warfare.
