Nilometer

This scale is located on Rawda Island in Cairo, and its construction is attributed to the year 742 AH by order of Caliph Al-Mutawakkil (737-742 AH). This scale was known by several names, including: the Hashemite scale, the new scale, the large scale, and the Rawda scale. It was built in a square with polished stones. Architectural description of the scale: This scale consists of a well, the construction of which increases in thickness as the depth increases. Accordingly, the well consists of three floors, the lower floor in the form of a circle, topped by two square floors, the third floor has longer and wider sides than the sides of the second square. It is worth noting that the thickness of the walls and their gradation in this way indicates that Muslims were aware of the engineering theory of the increase in horizontal pressure of the soil as the depth increases to the bottom. A staircase runs around the walls of the well from the inside, reaching the bottom. The scale is connected to the Nile by Three tunnels pour their water into the well through three openings placed specifically on the eastern side of the well so that the water remains still, as the movement of water in the Nile is from south to north and therefore there is no direction of movement of water in the eastern and western sides. These openings are topped with pointed arches resting on columns built into the walls with capitals and bell bases. In the middle of the well stands a stepped marble column with an octagonal section topped by a Roman capital 91 cubits long with measurement marks engraved on it. This column rests on a base of sycamore wood because it is the only one that is not affected by water to secure it from below, and is fixed from above by a beam-tie, and on it is an engraving in Kufic script of a Quranic mechanism that is considered the oldest example of archaeological writings in Islamic Egypt. The hand of reform and renewal has touched the Nilometer at different periods of time, including the reform carried out by Ahmed Ibn Tulun in 751 AH, which was recorded through inscriptions on the southern and western sides of the gauge indicating that he repaired the gauge and spent approximately 9111 dinars on it. During the reign of Caliph Al-Mustansir, his minister Badr Al-Jamali renovated the gauge in 425 AH and built a mosque on its western side known as the Mosque of the Gauge. The Mamluk Sultan Al-Zahir Baybars (852-828 AH) added a dome over the gauge well in the seventh century AH. Some reforms were also carried out during the reign of Sultan Al-Ashraf Qaitbay, King of Egypt (227-119 AH). It also witnessed other reforms during the Ottoman era at the hands of Sultan Selim I (192-178 AH), Sultan Suleiman the Magnificent (178-124 AH), and Sultan Selim II (124-127 AH). It also received a share of the efforts of the French campaign in 9794 AH/9211 AD, as they cleaned the well of the gauge from the silt accumulated at its bottom, and a piece of marble measuring one cubit was added to the gauge column and the date 9795 AH/9211 AD was engraved on it. In 9315 AH/9222 AD, the Ministry of Public Works cleaned the gauge again from the silt accumulated inside it. ·
The gauge engineer: The identity of the engineer who built the gauge is surrounded by some mystery. The historian Ibn Khallikan mentions that the gauge engineer was Ahmed bin Muhammad al-Hasib, however, some have mentioned that the one who built the gauge was an Iraqi engineer who was brought specifically for this purpose, named Muhammad Ibn Kathir al-Farghani, during the reign of Yazid bin Abdullah al-Turki. It was also said that his name was Ibn Katib al-Farghani and that he was a Copt.