Editing Nilometer (section)

==Designs==
[[File:Nilometer Rhoda Island Cairo June 1966.jpg|thumb|left|Conical structure covers the nilometer on southern tip of Roda Island in the Nile River at Cairo. The structure is modern but the nilometer dates from 715&nbsp;AD.<ref name="Fagan2010" />]]
[[File:Île de Roudah (el-Rôda). 1. Plan général du meqyâs ou nilomètre; 2. Plan du puits; 3. Coupe du nilomètre; 4-6. Détails de la colonne (NYPL b14212718-1268734).jpg|thumb|upright|Diagrams of the nilometer on Roda Island c.1800]]
The simplest nilometer design is a vertical column submerged in the waters of the river, with marked intervals indicating the depth of the water.<ref name="H" /> One that follows this simple design, albeit housed in an elaborate and ornate stone structure, can still be seen on the island of [[Roda Island|Roda]] in central [[Cairo]]<ref name="H" /><ref name="Fagan2010" /> {{nowrap|({{coord|30.0069|N|31.2250|E|type:landmark_region:EG_source:wikidata|display=inline|name=Rhoda Island nilometer}}).}} This nilometer visible today dates as far back as AD&nbsp;861, when the [[Abbasid]] caliph [[al-Mutawakkil]] ordered its construction,<ref name="Behrens-Abouseif1992">{{cite book|author=Doris Behrens-Abouseif|title=Islamic Architecture in Cairo: An Introduction|url=https://books.google.com/books?id=INsmT6zjAl8C&pg=PA51|year=1992|publisher=BRILL|isbn=90-04-09626-4|page=51}}</ref> overseen by the astronomer [[al-Farghani]]. Another nilometer had been ordered in 715 by Usāma b. Zayd b. ʿAdī, who was in charge of collecting the land tax (''[[kharaj]]'') in Egypt for the [[Umayyad Caliphate|Umayyad]] caliph [[Sulayman ibn Abd al-Malik|Sulaymān ibn ʿAbd al-Malik]].<ref name="Fagan2010" /><ref>{{Cite book|url=https://archive.org/stream/FP24037/08#page/n83/mode/1up|title=Tārīkh Madīnat Dimashq|last=Ibn ʿAsākir|pages=8:84}}</ref>

[[File:Assuan Elephantine Nilometer 14.JPG|thumb|upright|Nilometer on [[Elephantine|Elephantine Island]] ]]
The second nilometer design comprises a flight of stairs leading down into the water, with depth markings along the walls.<ref name=H/> The best known example of this kind can be seen on [[Elephantine]] in [[Aswan]],<ref name=H/> where a stairway of 52 steps leads down to a doorway at the Nile.<ref name="Farid">{{cite book |author= Farid Atiya |title= Pocket Book of Ancient Egypt  |url= https://books.google.com/books?id=LyWNFVeblO8C&pg=PA370 |page= 370 |date= 2008 |publisher= American Univ in Cairo Press |isbn= 9789771744399 |access-date= 2017-04-26}}</ref> This location was also particularly important, since for much of Egyptian history, Elephantine marked Egypt's southern border and was therefore the first place where the onset of the annual flood was detected.

The most elaborate design involved a [[canal]] or [[culvert]] that led from the riverbank &ndash; often running for a considerable distance &ndash; and then fed a well, tank, or [[cistern]].<ref name=H/> These nilometer wells were most frequently located within the confines of [[temple]]s, where only the priests and rulers were allowed access. A particularly fine example, with a deep, cylindrical well and a culvert opening in the surrounding wall, can be seen at the [[Temple of Kom Ombo]], to the north of Aswan.