Misconceptions for Risks of Coastal Flooding Following the Excavation Of

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N° 108 - 2007 37 Misconceptions for risks of coastal flooding following the excavation of the Suez and the Corinth canals in antiquity Méconnaissance des risques de submersion littorale et creusement des canaux de Suez et de Corinthe dans l’Antiquité

Stathis C. STIROS Department of Civil Engineering Patras University Patras 26500, Greece e-mail: [email protected]

Abstract - During antiquity, numerous attempts were made to excavate Résumé - Durant l’Antiquité, de nombreuses tentatives ont été effectuées canals through the Suez (Egypt) and the Corinth (Greece) isthmuses, but these afin de percer les canaux de Suez (Egypte) et de Corinthe (Grèce). Elles se sont projects were never completed. The main explanation provided by historical toutes soldées par des échecs. La principale raison retenue par les sources sources is the risk of flooding of coastal areas by water flowing through these historiques est la question des différences de niveau marin de part et d’autre canals, since an up to 10 m difference was assumed to exist at their inlets. des isthmes qui furent évaluées jusqu’à 10 m. Par conséquent, les Anciens Obviously, such considerable elevation offsets which would also render the craignirent d’établir des canaux non praticables du fait de l’importance des canals non-navigable due to a continuous flow of water, reported to derive courants et d’inonder les zones basses adjacentes. Il semblerait que tous from leveling measurements. Examination of the evidence reveals that such ces risques ont été volontairement exagérés par les détracteurs des canaux. large errors in ancient geodetic surveys are unlikely, but there exist important Certains notables ont vraisemblablement profité de l’abandon des différents differences in the tidal ranges and the coastal environments on either side of projets. Les deux canaux ne seront finalement percés qu’au XIXe siècle. the two isthmuses. It appears therefore that the impacts of minor water flow Depuis leur ouverture, les canaux fonctionnent normalement et témoignent from one side of the canal to the other, observed in the modern canals, were de l’absence notable de différence de niveau de la mer de part et d’autre de exaggerated during antiquity by detractors (especially the risk of flooding), leurs embouchures who eventually succeeded in getting the projects abandoned.

1 - Introduction suggest that the plans for such impressive works were mostly abandoned because geodetic studies revealed a 10 m difference in sea-level elevation at their inlets. In light of this, it was hypothesized that excavation of both canals would lead to flooding of the low-lying coasts, while the expected continuous flow of water from one inlet to the other would hinder ship navigation. This postponed the construction of the canals until the nineteenth century; since this time the canals operate without locks, confirming the absence of significant sea-level differences (Lewis, 2001). Such gross errors in leveling appear surprising, given that engineers in ancient Greece and Egypt were notorious for their mastery of surveying techniques. These skills are for instance epitomized first by the ~1000 m long tunnel of Eupalinus (Samos Island, Aegean Sea), successfully excavated in ~540 BC (Kienast, 1995), and second, by qanats. The latter, widespread in the Middle East and not uncommon in the Mediterranean, Fig. 1 - Location map. are underground sub-horizontal water channels up to tens of Fig. 1 - Carte de localisation. kilometers long, excavated at the bottom of deep wells (English, 1998; Stiros, 2006). Stiros (2006) has shown that ancient During antiquity, a number of major engineering works, surveyors were able to obtain high accuracies in leveling. requiring high technical and geodetic skills,�� was undertaken. This makes geodetic errors unlikely for the Suez and Corinth These included projects to build the Suez canal in Egypt and canals. In light of this, we re-evaluate the available information the Corinth canal in Greece (Fig. 1), both eventually completed concerning the early history of these two canals, and try to during the nineteenth century. The reasons for the failure of shed some light on the real causes of their abandonment in the projects were not a lack of funding, changes in the political antiquity, as well as on the misconceptions for the threat of situation, or unresolved technical problems. Historical sources coastal flooding following their excavation 38

2 - The suez canal up to foreign invasion. Pliny also noted that some feared contamination of freshwater reserves by saline Red Sea water (Pliny, Natural History VI 33). For these reasons only the part of the canal from the Nile to the Bitter Lakes, 34 miles long, was completed (Fig. 2). Inscriptions on ��a number of granite stelae state that “I ordered the canal to be dug up from the River called Pirava (the Nile), which follows in Egypt to the sea that comes out of Persia (The Red Sea)” and suggest that the canal to the Red Sea was completed by Darius. In reality, it appears that the connection between Bitter Lakes and the Red Sea was made over land, using camels and horses. This interpretation is supported by the fact that a canal was excavated in the area ��during the Ptolemaic (Hellenistic) period ~270 BC, with the construction of a lock to counteract the expected flow of water. The town of Arsinoe was founded at the canal’s inlet, near present-day Suez�� (Fig.�� 2). The ancient canal was repaired by the Roman emperor Trajan ~100 AD, and was extended to meet the main branch of the Nile Fig. 2 - Location map of the Suez canal area. Names in italics denote ancient near Cairo (Fig. 2). It remained navigable until the 3rd century sites. Dashed lines with numbers in circles indicate partially excavated AD, while repairs were made to the southern branch between sections of the ancient canal during 1: Pharaonic and Persian times (up to 500 BC); 2: Hellenistic times (~270 BC); 3: Roman times (~100 AD). the Bitter Lakes and Suez. The exit of this canal was not at Fig. 2 - Carte de localisation de la région du canal de Suez. Les noms en Arsinoe, but a few kilometres to the west. The Roman canal italique correspondent aux sites antiques. Les pointillés avec des cercles soon silted up, but was again re-opened in the seventh century localisent les secteurs creusés durant : 1. Périodes pharaonique et perse (jusque vers 500 avant J.-C.) ; 2. Période hellénistique (vers 270 avant J.‑C.) ; AD by Amr ibn al-Aas, the Arab conqueror of Egypt, and 3. Période romaine (vers 100 après J.-C.). came to be known as the “Canal of the Commander of the Believers to the God.” Amr ibn al-Aas planned its extension The present-day Suez canal, completed in 1869, represents a to the Mediterranean, but his project was dropped on military system of artificial water channels and lakes along the isthmus grounds (the fear that it would facilitate invasions), and for connecting Asia and Africa, and separating the Red Sea from these reasons the canal was closed in 776 AD. the Mediterranean. The isthmus is about 160 km long, of low Shortly after the opening of marine routes around Africa in elevation and flat-topped (Fig. 1a) and has been formed by Late the fifteenth century, the Venetians drafted the first modern Quaternary tectonic uplift (cf. Jackson et al., 1988; Gvirtzman, plans for a Suez canal to shorten the distance to India; work 1994). was resumed by Napoleon around 1800. Yet again, however, his engineers estimated a 10 m elevation difference between 1.1 - Historical and archaeological background the Red Sea and the Mediterranean. The result was debated by The construction history of the Suez canal is unclear, but Fourier and Laplace, famous mathematicians and physicians has been summarized by various authors (e.g. Marlowe, 1964; of the period, but nonetheless served as a catalyst to the Lewis, 2001). Plans for a navigable channel in this region are abandonment of Napoleon’s project. Interestingly, parts of the very old, with ancient reports and archaeological remains ancient canal were used as an aqueduct bringing fresh water for indicating that an early canal had been excavated in the isthmus the workers and the engineering works during the construction 2-3,000 years ago. of the modern canal (Marlowe, 1964; Lewis, 2001). The first historical report is that of Aristotle Meteorologika( 353b), the famous fourth century BC philosopher, who 1.2 - Reconstructing the history of the ancient reported that Pharaoh Seti (or Sesostris, around 1300 BC) canal and the Persian king Darius, who occupied Egypt in circa The available historical, archaeological and geomorphological 500 B C, tried to excavate a canal similar to the present-day data allow us to suggest that the geomorphology (a low-altitude, one. Their projects were, however, abandoned due to fears over flat area) and the geology (soft Quaternary and Holocene freshwater contamination by saline water caused by flow of sediments) of the Suez isthmus facilitated early plans for an saline water due to altitudinal differences between the Red Sea irrigation channel between the eastern (Pelusiac) branch of the and the Mediterranean. Interestingly, a channel mentioned in Nile near the town of Bubastris, to the swampy area of Lake an inscription at Karnak, dating from Pharaoh Seti’s reign, is Timsah and the Great Bitter Lake (Fig. 2). This was a sizeable usually taken as evidence of an early Suez canal. task for, as can be seen in the satellite photo (Fig. 3), the Around 100 AD, the Greek historians Diodorus Siculus channel was to be excavated along stable, low-elevation ground (Historical Library 1, 33.9-10), Strabo (Geography XVII 1.25) following an E-W trending abandoned branch of the Nile River and the Roman historian Pliny (Natural History VI 33), probably (Wadi Tumilat) flowing into the Red Sea. This channel closely citing older information, reported efforts to excavate a canal resembled the present-day canal, and its main, if not its sole by Pharaoh Sesostris or later by Pharaoh Necho II (~600 BC), function was irrigation. It is likely that it was completed around and then later by Darius around 500 BC, were abandoned due 600 BC (during the reign of Pharaoh Necho), and was probably to the risk of flooding of Lower Egypt. Another possibility is the only channel constructed during Pharaonic times, given the astrologers warned that the channel would open the country need for irrigation and flood control. 39

this conclusion. Because of the silting up of the Nile’s eastern (Pelusiac) branch, it is likely that during Roman times (Trajan’s reign, ~100 AD), it became necessary to excavate a N-S extension canal from Bubastris to the main branch of the Nile at the town of Babylon, modern Cairo (Fig. 2). The path of the Suez section was also modified, reaching the sea at the town of Clysma, some kilometers west of Arsinoe. The elucidated history of the ancient canal is a reasonable one, though variations on this version are presently debated by historians and archaeologists. What is important, however, is that the construction of irrigation channels was welcomed by everyone. Nonetheless, the plans for a navigable canal were delayed by detractors (mostly astrologers and geodesists) for many millennia!

1.3 - Accuracies of ancient geodetic surveys Modern science does not permit us to evaluate the conclusions of astrologers in the Pharanoic court, who were apparently opposed to the construction of the navigable channel. However, it does allow us to evaluate the results of ancient surveyors who are supposed to have measured a 10 m altitudinal offset between the two inlets of the planned canal. Measurements for Darius’ canal were probably made by his engineers, who first introduced qanats to Egypt. His engineers, well-trained in leveling long distances in arid areas, were definitely able to obtain accuracies of 1-2 m over distances of 100 km on flat terrains. Stiros (2006), based on the analysis of qanats, concluded that even using primitive instruments ancient surveyors were able to measure elevation changes over long

distances with standard errors �σΔh� defined by the formula(1)

σΔh� =� �σo � √S where S is the length of the leveling route in kilometers and

σo =�0.45- 0.03m/√km. For a distance of 160 km (i.e. equal to the length of the isthmus), a standard error of 0.5- 5 m can be estimated. Such impressive accuracies, obtained after repeated and time-consuming measurements, obviously exclude the possibility of leveling errors of 10 m along the Suez isthmus, especially considering the survey was made over totally flat and uniform terrain. Fig. 3 - Satellite view of the Suez area. Grey zone marked represents Wadi Tumilat, a cultivated, low-elevation corridor through which the�� first irrigation On the contrary, the survey by Napoleon’s engineer canal was excavated around Lake Timsah. J. Lepréduring during the nineteenth century, although Fig. 3 - Image satellite présentant la zone de Suez. La dépression du corridor based clearly on higher accuracy leveling instruments (i.e. de Wadi Tumilat (zone grise) correspond à la première zone de creusement du canal dans la région du lac Timsah. instruments with an alidade and bubble levels), led to an error of nearly 10 m (29 feet). This difference can be explained by the After the mid first millennium BC, when the need for a marine fact that the French engineer was not acquainted with refraction passage between the Persian Gulf and the Mediterranean errors, a major source of error in arid climates (Bomford, 1971; became necessary, a second navigable channel was excavated Vanicek et al., 1980; Strange, 1981; Stiros, 2006). It appears from the Bitter Lakes to the Red Sea. This broadly followed the that his measurements were severely affected by systematic path of the southern segment of the modern canal from the Bitter errors. The correct elevation difference was finally computed Lakes in the north, to the Suez, on the Red Sea coast (Fig. 2). in 1846-1847, as a result of surveys made by the French Society Plans for an extension of this channel to the Mediterranean for the Study of the Suez Canal. were, however, never realized. Persian period inscriptions commemorating the construction 1.4 - Sea level marks of a navigable canal (see above) seem to indicate a waterway The estimation of sea-level differences on an isthmus is based completed under Darius’ reign. However, it is more likely that not only on leveling measurements, but also on the identification ~500 BC Darius rendered the northern part of the waterway of the necessary reference levels. Such levels in the modern navigable from Bubastris to the Bitter Lakes only, and that hydrographic literature are known as Mean Sea Level (MSL), the southern section from the Bitter Lakes to the Red Sea was Mean Low Water (MLW), Low Water Line (LWL, used as a completed later, around 270 BC by Ptolemy. The foundation reference level by port authorities), High Water Level (HWL) or of Arsinoe at its inlet, near present-day Suez (Fig. 2), supports Mean High Water (MHW). The above levels can be identified 40

on the basis of either tide-gauge observations, or biological up to 80 m high. These favorable engineering conditions were and morphological data (Parker, 2003; Leartherman, 2003). known to the ancient Greeks and the first plans for a canal Although tide-gauges are known to have been used to monitor were probably made as early as 600 BC, at a time when ancient the level of the Nile (the “nilometer” has been in use since at least Corinth flourished. the eighth century BC) and are described by Strabo and other Historical accounts suggest that Dimitrios Poliorkitis, the authors, we can reasonably assume that ancient geodesists and most prominent successor of Alexander the Great, first tried to engineers have probably relied on non-instrumental evidence open the Corinth canal ~300 BC. He was advised by Egyptian to identify reference levels (“datums”) for their calculations. experts who stated that, due to the higher elevation of the Modern data reveal that the difference in mean sea level Corinthian Gulf, water flow would drown islands in the Saronic between the two canal inlets is practically nil. There is, Gulf (Aegean Sea). Interestingly, Strabo also refers to a debate however, a significant difference in the tidal ranges: ~10 cm between the ancient geodetist Eratosthenes, who proposed an in the Mediterranean and up to 2.7 m in the Red Sea (Bourdon, alternative concept to Archimedes’ work on fluids Strabo, ( 1925). Even if it is assumed that ancient engineers based their Geography, 1 3.11,14), to suggest that uneven sea levels could measurements on the Mean High Tide Level, i.e. levels that exist even over relatively short distances. can be easily identified on the basis of geomorphological and Roman emperors Julius Cesar and Caligula are thought to biological observations (Pirazzoli, 1996; Morhange et al., have planned the excavation of the canal. The most important 1998; Stiros and Pirazzoli, 2004), this only accounts for ~1 m works were, however, undertaken by Nero, in 67 AD, using of error. captives from the Jewish War. Logistic difficulties meant that Since the two errors (i.e. leveling and sea level) are not the project was eventually abandoned (Gerster, 1884), although correlated, according to the law of error propagation (e.g. partial remains of this early excavation are still visible. Two Bomford, 1971), the total error ��σ�� can be calculated from the later reports refer to the efforts of Nero. The first, by pseudo- formula (2) Lucian (pseudo-Lucian, Nero IV) written ~200 AD cites 2 2 2 σ =� �σ � leveling+�σ sea level Strabo’s explanations for the causes of the interruption of the This leads to a standard error of around 5 m. In light of this, works. The second, by Philostratus, a Greek writer around 220 a 10 m elevation difference seems too large even if both AD repeats the same scenario, but cites political instability as the datum (i.e. deriving from the identification of the mean the cause for abandonment of the project (Philostratus, Life of sea level) and leveling errors are taken into account. Appolonius of Tyana, IV 24). The final excavation was started in 1881 and was completed in 1893.

2 - Corinth Canal 2.1 - Accuracy of geodetic surveys Corinth isthmus, 6.2 km long and more than 80 m high, The Corinth isthmus is 6.2 km long and ~80 m high in its comprises a horst of faulted and uplifted Pliocene and central part, with a smooth relief. On the basis of equation (1), Quaternary sediments at the eastern edge of the Gulf of the possibility of an important elevation error in between the Corinth graben (Freyberg, 1973; Mariolakos and Stiros, 1987). two exits of the canal is very small. The isthmus linked the Greek mainland to the Peloponnese, and served as a physical barrier to marine traffic. Significantly, 2.2 - Sea-level marks it isolated the Gulf of Corinth from the flourishing regions of the Aegean, in addition to southern Italy and Sicily (Fig. 1). Due to its strategic position next to the isthmus, the town of Corinth flourished in ancient Greek and Roman times. The city was served by two harbours: (1) the eastern harbour of Kenchreai in the Saronic Gulf; and (2) the harbour of Lechaion in the Gulf of Corinth (Fig. 4). The latter was the first artificial harbour to be constructed, probably around 600 BC (Stiros et al., 1996). During the mid first millennium BC, a paved ramp (“Diolkos”) was constructed along the isthmus, permitting ships to be transported from one side to the other. This ramp followed the path of the present day canal (Fig. 4), and some of its remains are still visible today (Verdelis, 1956). Diolkos made Corinth very wealthy, but apparently could not meet the needs of commerce and communication. For this reason plans to excavate a canal were conceived early in Fig. 4 - Satellite view of the Corinth area, Greece. The Canal excavated at antiquity. The Xerxes canal was excavated at the NW edge of the end of the 19th century is shown. A minor current from the Gulf of Corinth the Aegean for military purposes during the Persian Wars (~480 (to the west) to the Saronic Gulf (to the east) is observed, but is too small to represent a threat for flooding of the Saronic Gulf, as was argued in BC) and attests to the potential for major engineering projects antiquity. in ancient Greece (Isserlin et al., 2003; for location see Fig. 1). Fig. 4 - Image satellite de la région de Corinthe. On voit clairement le canal The major advantage of the Corinth isthmus is that it was creusé au XIXe siècle. Un léger courant marin s’écoule du golfe de Corinthe à l’ouest en direction du golfe Saronique à l’est. Durant l’Antiquité, certains built of very coherent Pliocene and Quaternary sediments, auteurs pensèrent que ce courant aurait pu submerger les rives du golfe mostly marls, which permit excavation of subvertical walls Saronique. 41

As is the case with the Suez isthmus, there is no significant Lakes and the Red Sea, in which a fauna and flora different to difference in sea level, but significant differences in tidal that of the Mediterranean exists (Por, 1971). As Pliny noted, level do exist on either side of the Corinth canal, with tide a flow of water from the Red Sea towards the Bitter Lakes, gauges recording a mean tide of 0.30 m in the Gulf of Corinth Wadi Tumilat, etc. (Figs. 2, 3) threatened to contaminate the and 0.08 m in the Saronic Gulf (Zoi-Morou, 1981). Even if it freshwater reserves. is assumed that ancient engineers used the high tide mark Thus, two groups were opposed: (1) those trying to open and not the mean sea level as their datum, the difference is marine routes for financial and military reasons, and kings only around half a meter. Such a discrepancy is obviously too wishing to associate their names with important works; and small to drown the Saronic (Aegean Sea) coasts, although it (2) farmers, worried about the contamination of freshwater can produce a constant current. A permanent, slow current is reserves, fishermen, some military officers and those living indeed observed in the modern canal. from traditional trade. It is therefore likely that the abandonment of the early project for a complete Suez canal in antiquity was not 3 - Discussion due to a “geodetic error”, as is widely accepted, but rather to detractors’ exaggeration of hydrographic and ecosystem Debate over sea level differences between the two inlets of the differences either side of the isthmus leading to a fear for Suez and the Corinth canal, both leading to the abandonment flooding of coastal areas. In the case of Corinth, the contrast of these projects in antiquity, present a number of similarities: in the physiographic and hydrographic conditions at the two (1) Measurements by Egyptian engineers are assumed to have inlets of the planned canal was minor. The possibility of led to significant sea-level offsets between the two inlets of an error in the sea-level estimations was moderate. The the planned canals. It was hypothesized that such differences abandoned Suez project and observations at the Euripos Strait, would lead to the drowning of “low-lying” coastal areas. (2) in combination with the huge amount of material to be excavated Significant differences are observed in tidal levels either side for the canal (walls up to 80 m high) led to the collapse of the of the two isthmuses, and such differences do produce weak Corinth project. currents. (3) Although important in the 1800 survey, the leveling errors cannot explain the reported elevation differences in sea level measured in antiquity. 4 - Conclusion Ancient engineers were certainly aware of water flow along channels, as attests the example of Euripos Straits in Central It is usually assumed that gross (up to 10m) errors in Greece (Fig. 1). In fact Strabo mentions that Eratosthenes, a leveling revealed a considerable difference in sea-level at the famous 3rd century BC geodetist, had attributed the flow to two inlets of the Suez and the Corinth canals, and this led to differences in sea level on either side of the straits (Strabo, 1, fears that (1) a continuous flow of water would render both 3, 12, 36, 55). This provided an alternative explanation to that canals non-navigable, and (2) it would lead to drowning of of Aristotle, who in his Meteorologika had assigned flow to coastal areas. Such fears are assumed to have prevented the hydrodynamic effects. Archimedes suggested that sea waters excavation of the two canals during antiquity. Examination of follow the laws of ideal liquids, and hence excluded the the evidence reveals that such large of errors are unlikely in possibility of uneven sea levels supported by “geodesists” such the ancient geodetic surveys. More important is the contrast in as Eratosthenes (Strabo, Geography, I, 3, 14). Interestingly, hydrographic and physiographic conditions at the two inlets of similar debates arose in the nineteenth century, with famous the canals. These differences fuelled debates on water currents mathematicians and physicians such as Laplace and Fourier through the planned canals. Exaggeration of possible negative rejecting the geodetic measurements along the Suez canal on impacts, in particular of the risk for flooding of coastal areas, the basis of physical laws (see Marlowe, 1964). was used by detractors to force the abandonment of the projects It appears therefore that the heart of the problem is not during antiquity. the geodetic measurements but rather the corresponding hydrographic conditions, and notably differences in tidal range. 5 - Acknowledgements There is another parameter which has a role to play, at least in the case of the Suez canal. Partly due to sea-level variations We thank Eva Stirou for assistance with drawings and (Gvitrzman, 1994), several lagoons exist between the Bitter bibliographic research.

6 - References

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