Nilometers were used in Egypt, particularly during the Pharaonic, Roman and medieval periods, to measure the Nile’s water level during the annual summer flood. Essentially, apart from such ritual functions they may have served in ancient Egypt, nilometers worked on the Goldilocks principle as far as the rulers of Egypt were concerned. If the water level in August–September was too high, the effects on the narrow band of fields either side of the river, and the surrounding infrastructure, would be devastating and there was no point sending out the tax collectors. If the water level was too low, the population would starve, and there was also no point sending out the tax collectors. If the water level was just right, a rich layer of alluvial silt would be deposited as the flood subsided, crops would grow, and off would go the tax collectors, no doubt singing merrily to themselves.
The structures were of three types: a simple vertical column in the water (as in the medieval example in central Cairo, the modern ornate housing of which is pictured above); a well with a culvert to the Nile (as, supposedly, at Kom Ombo temple, although this may simply be a well rather than a measuring device); or a set of steps cut into the bank (as at Elephantine Island, Aswan). Each was calibrated in Egyptian cubits (roughly 54 centimeters or 21 inches) subdivided into seven palms, and then into four fingers.
The medieval nilometer at the end of Roda Island in Cairo—though of the simplest type—is particularly beautiful with its nineteenth-century Turkish conical roof, though, as a rather small uninteresting building from the outside, it is often overlooked even by those who have lived in Cairo all their lives.
Standing on the site of an older building (destroyed in AD 850, ironically enough, by the Nile’s flood) from AD 715, and probably on the site of a Pharaonic nilometer, the current structure dates to 861, when it was ordered to be built by the Abbasid caliph Al-Mutawakkil under the direction of Ahmad ibn Muhammad Al-Hasib. It was restored by Ibn Tulun in 872–73, and again in 1092 by the Fatimid caliph Al-Mustansir.
The architect of the existing structure, Abu’l ‘Abbas Ahmad ibn Muhammad ibn Kathir Al-Farghani—rather more pithily known in the west as the astronomer Alfraganus—was a native of Farghana, in West Turkistan (now Uzbekistan), an important staging post on the North Silk Road from Xi’an. There is a statue dedicated to him at the entrance to the Roda Island site.
Alfraganus’s design was quite straightforward. Three tunnels at different heights lead in from the river to the east into a stone-lined pit around a central marble column, resting on a large millstone and capped with a Corinthian capital, marked in 19 cubits. Thus, the nilometer was capable of measuring a flood of 9.2 meters. If the flood measured much below 16 cubits, it was too low, and if it measured above 19, it was too high.
In the days immediately preceding the maximum flood, the column was anointed with saffron and musk in order to help induce the most beneficial water level.
In addition, around the top of the pit are talismanic Qur’anic inscriptions in Kufic script (said to be the earliest surviving examples of architectural epigraphy in Egypt):
“We sent down water from heaven as a blessing, causing gardens to grow, and grain for harvest” (50:9).
“See you not how God sends down water from heaven so that the earth becomes green?” (22:63).
At one time, a short dedicatory inscription, indicating that the nilometer was built in 861, completed the frieze. This was removed in 872 and replaced by more Qur’an inscriptions, probably by Ibn Tulun as a means of asserting his independence from Abbasid Baghdad.
The stone-lined pit—circular at the bottom and rectangular at the top—is accessed by a staircase hugging the interior wall. At one level the walls have recesses on each side with pointed arches and framed by thin columns, decorated with zig-zag patterns. These ‘tiers-point’ arches are, remarkably, of the same type that would characterize Gothic architecture in Europe some three hundred years later than their appearance here.
In the medieval period, and possibly before, the moment the Nile flood reached 16 measured cubits along the vertical central column was a key moment for celebration. This was the signal for the Festival of the Opening of the Canal at Fumm Al-Khalig (the mouth of the canal). The Khalig lay along modern Port Said Street and consisted of a narrow waterway that bisected Cairo from south to north until it was finally paved over in 1898.
The Khalig was dry for most of the year, and, certainly in its later years, widely considered a health hazard. Cesspit workers were employed to clean the canal every year by hand, and as late as 1870 a petition was presented to the Ottoman authorities urging them to do something about the awful stench and “forestall the possibility of an epidemic.”
Nonetheless, John Gardner Wilkinson (1797–1875), considered by many to be the father of British Egyptology—he first numbered known tombs in the Valley of the Kings from KV1 to KV21, among other achievements—wrote extensively about the Festival in the 1847 Handbook for Travellers in Egypt, published as part of the well-respected John Murray handbooks for travelers (a series which eventually mutated into my all-time favorite set of guidebooks, the Blue Guides).
On the night before the festival, according to Wilkinson, thousands of Cairenes crowded booths on the shore or boats on the river where they were suitably entertained. Marquees were also pitched along the north bank of the canal for the Governor of Cairo and other dignitaries.
At about 8 am on the morning of the festival, the governor would arrive with his troops and attendants, and upon a signal, men would cut the dam holding back the Nile with hoes. A pillar of earth, ‘Arousat al-Nil’ or ‘The Bride of the Nile,’ would be left in the middle of the dam which, tradition held, was a substitute for a human sacrifice to the river gods in Pharaonic times.
While the flood rushed into the canal, the governor would throw silver coins, and the men who had cut the dam would dive into the rapidly swirling water to retrieve them, with the occasional unfortunate result.
As soon as sufficient water had entered the Khalig, boats full of Cairenes would pass through the canal.
This no-doubt colorful spectacle came to an abrupt end, of course, when the Khalig—which was a particularly noisome ditch running through the center of the city for most of the months of the year—was paved over (and became the first tram line in Cairo).
After the initial damming of the Nile at Aswan in the early twentieth century, nilometers
also began to fall out of use, and, indeed, the fine example on the end of Roda Island no longer connects to the river at all, though it may have done so as late as 1970.