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· Egypt, the gift of the Nile Egypt would not exist without the river and its periodical flooding which regulated life, work in the fields, religious and civil feastdays. The banks flooded by the river when it was in spate were transformed into arable lands. Before the great modern dams were built, the average width of these banks varied between 100 m in Sudanese Nubia and 1000 m in Egypt. The floods were devastating when a certain limit was exceeded, when they were very late or when the floods did not reach the minimum required level. It is nearly always towards the 10th June that the Nile starts to rise, rolling its "green waters" full of the decomposed grasses from the great equatorial lakes. But the river rises almost imperceptibly and its waters are unhealthy. It is in the middle of July that the rise in water level becomes evident due to the "red waters" from the disaggregation of the rocks from the torrents of Ethiopia which are driven towards the Nile by the violent summer storms. At the end of August the river is in full spate and maintains its highest point until about 7th October. The level then goes down gradually without any abrupt oscillations.As in all alluvium valleys, the Nile's banks are higher than the plains which stretch from each side of its bed and which dip towards the mountain chains along the desert. The river's overflowing water would thus rush towards the low terraces and transform them into immense lakes (Gaston Migeon, Cairo, 1909). Thanks to this cycle of flooding, the Nile regulated life and determined the calendar. The nilometre according to StraboStrabo (about 58 BC-21/25 AD) gave the following definition of a nilometre: "the nilometre is a well built of squarred stones in which are marks indicating the flooding of the Nile, because the water in the well rose and fell in line with the water of the river. That is why there are marks on the wall which are examined by inspectors and their observations are passed on to the rest of the population. Indeed, they know well in advance, from these signs, when the next flooding is going to take place. This information is useful to the farmers and for regulating the distribution of public revenue, as the revenues are higher the greater the flood". (Geography, XVII, 1). · Historical background The nilometres of ancient Egypt were still used for at least half-a-century after the Arab conquest of the country by Amr Ibn Al As who repaired some of them, such as those in Aswan, Dendera and especially in Halwan (25 km from Cairo, above Memphis on the right bank of the Nile). Some historians attribute the construction of the well to him, while others, on the contrary, attributed it to Abdelmalek Ibn Marwan, the Ommayad Caliph of Damascus in 699 AD. The nilometre of Halwan, restored or built entirely in 699, was shortlived as already in 714, 17 years after its presumed construction, it was in such a bad state that the Caliph of Damascus, Al Walid Ibn Abdelmalik, decided to have it replaced by a new one and ordered the governor of Egypt to see to it near Fostat. The work was done extremely quickly and the new well was completed in 715 under the reign of Soliman who had just succeeded Al Walid. This is the Ar-Raoudha nilometre whose site was judiciously chosen on the tip of the island which still bears his name today. ·Chronology: 714-715: first works overseen by Oussama Ibn Zayd at-Tannoughi, the tax official (kharadj). 814: renovation under the Abbasid Caliph al-Ma'moun. 847 and 86 : great works undertaken twice more under the Abbasid Caliph al-Moutawakil and the last works were supervised by the engineer Ahmed Ibn Mohamed al-hassib.Abdallah ar-Raddad from Basra in Iraq was responsible for its management as the designated official for the "miqiyas" and this job remained in his family for centuries. 1092 : last great works by the Fatimid al-Mustansir who added the nearby mosque. After the end of the XIth century under the Seljukides and the Mamelukes, no works of great importance were undertaken, except perhaps under Baybars and Qaitbey. It was not until the reign of the Ottomans, Selim I, Soliman the Magnificent and Selim II that restoration work was carried out again. Recorded work was done in 1756, then during the French expedition (1798-1801). In 1887 the Ministry of Public Works restored the monument and added a pyramidal cupola in 1925. Recent exhaustive work restored the monument to its former splendour. This permanent attention paid to the monument during thirteen centuries of its existence at least bears witness to the importance it had for the governments throughout the different periods of time. · The Monument There are two basic parts: - the 3-storey well and in its axis the graduated marble pilaster, the instrument for measuring the flood. - Tunnels which communicate with the Nile through three openings, each opening is on a storey and turned towards a direction different from the other. The well is in a deep square hole dug to at least a depth of 13 m and 10 m wide, necessitating the removal of at least 1300 m² of earth and hard clay. The construction was raised on a foundation made of thick tree trunks, which stabilized the construction and stopped it from sinking into the clay. On this socle are the stone foundations which are circular in shape on the first storey, where there is the first connection with the Nile through a first tunnel with a barrel vault oriented towards El Fostat (south-east). Then there is the second, square shaped storey, much larger than the one below and connected to the Nile through a tunnel oriented this time towards the east. Finally an even bigger third storey communicating with the Nile through a tunnel. The whole construction is built of finely cut stone. Stairs close to the walls surround the circular space at the bottom and around the square shaped two storeys, and in the central axis rises a marble octagonal pillar graduated in cubits and in digits to gauge the water level. The following conclusions can be drawn from this description proving the exceptional importance of the monument: 1°) the engineer, doubtlessly heir to the well-established and remote Egyptian tradition of hydraulic constructions, (the previous description is reminiscent of that of Strabo in the 1st century BC) and especially that of nilometres, knew how to find the most appropriate solution to solve the thorny problem of pressure exerted on the walls of the structure; external pressure due to the movements of the Nile and internal pressure due to the rising water. 2°) This monument from the Arab period, the oldest in Egypt after the 'Amr Mosque in Cairo, has epigraphic texts, the oldest of which is the double frieze on the northern and eastern sides, inside the cage with the name of the person who supervised the works in 861, Ahmed In Mohamed al-Hassib. This is indeed the first inscription on a monument in Egypt from the Moslem period which is still intact. 3°) The pointed arches with two angles which crown the four depressions in the four walls of the upper storey and the bases of the bell-shaped corner columns, are the oldest we have in Egypt. 4°) The construction of this masterpiece of Moslem architecture which reflects one of its first Egyptian manifestations, was a real technical feat as it had to be built extremely rapidly within six months which separate the period when the Nile is at its lowest and the period when the Nile starts rising and overflows. The builders presumably therefore must have had the necessary expertise and experience. · Description of Leo Africanus (end of XVth century beginning of XVIth century)In the middle of the Nile facing the old city of Al-Fostat, is an islet called the "al-Miqiyas islet" because it contains the instrument for measuring the levels of the Nile. This island is highly populated and has a big mosque, most pleasant as it faces the bank of the river. Beside it is an isolated and closed structure from the middle of which arises a pillar marked with 18 cubits. At the bottom of this deep well are underground canals which communicate with the river. When the Nile starts rising the water penetrates the canals and starts rising, two digits in one day, three digits another day. Experts come every day to read the water level indicated on the pillar"."The Nile rises for forty days and then starts sinking for another forty days. During that period there is a reduction in foodstuffs which everyone starts selling secretly at any price they want until the prices are fixed officially. This happened once a year and the officials had to make a distinction between well watered areas, those less well watered and those which were overflooded, depending on the nature of the terrain in which the farm was situated. The price of bread was fixed in accordance with this data".It was a fact that the year would be a good one if the pillar recorded 15 cubits and a bad one if it recorded between 12 and 15 cubits. When the level was between 10 and 12 cubits, the price of wheat cost ten mithquals and one kil. When the level exceeded 18 cubits the shops, boutiques, houses and fields were faced with the risk of flooding. The children, with yellow turbans, then started running in the streets to alert the population. The Ar-Raoudha nilometre, the most important of all those built by the Arabs on the Nile, lasted the longest, has come down to us in a perfect state of preservation and is also the best documented. 1°) It was minutely described by the travellers who visited it as well as by the geographers and historians who often recorded the repairs and restoration work carried out. The scientific mission which accompanied the French expedition from 1798 to 1801, made a good and exhaustive study of it (its history, architecture, mode of functioning, rises in water level, economic aspects etc.) within the framework of a voluminous book on the description of Egypt. "I can say, wrote in 1800, one of the members of the French mission, that this monument is the most important of all those ever built in Egypt by the Caliphs, not only because of the numerous inscriptions and their good state of preservation, but above all because of the role it played and the links it always had with the price of foodstuffs and State revenue". This "thermometer" made it indeed possible not only, for at least thirteen centuries, to gauge the changing and capricious moods of the greatest river in the world, but also the hazards in the life of the people, starting with the leaders at the top right down to the humblest social categories. The Raoudha nilometre is thus an eminent example of a type of construction, a technology, architecture and art illustrating a significant period in the history of Egypt and the Moslem world. It is perfectly preserved and is the last one in Egypt of a great line of nilometres whose history is intimately linked to that of Egypt. It is of great symbolic and sentimental value linked to the Nile, for the people of Egypt.