Frequently Asked Questions
What kind of technical equipment do you use for your research?
Different kinds of techniques are used during our research and with the fast pace of technical development we are also continuously updating our equipment. We have used a combination of technology over the years such as echo sounders, side scan sonar, multi-beam sonar, NMR magnetometer, sub-bottom profiler, and parametric sub-bottom profiler, to provide non-intrusive survey data. You can see from this list that we have moved with the times as survey technology has developed so that we are always using cutting edge methods. For instance, Franck Goddio is currently developing an intelligent programme out of his pool of geophysical data and underwater excavations to help identify targets from the huge amount of data from our latest surveys using the parametic sub-bottom profiler. We have also changed the way that we record the things that we excavate over the past few years, moving on from traditional hand drawings underwater using tape measures and pencils to now using photomosaics and 3-D underwater photography.
For a full list of technical equipment and explanations please click here:
Did you also find bones during your excavations?
Yes, in Thonis-Heracleion we found ox bones as well as giraffe and hippopotamus bones. As they don't seem to be sacrificial animals, or the butchered remains of food, we think that there might have been a zoo on the site! The bones are currently studied in more detail to find out more about this suggestion.
How deep were the dives where objects were found in Thonis-Heracleion?
Dives are between 6 to 10 metres (19.6 to 32.8 feet) depending on where you are in the city. Additionally, we excavate deep into the sediment, which can add a further 3 to 5 metres (9.8 to 16.4 feet) onto the depth of the dive.
Do you try to bring up all objects you find? If not, how do you decide what to recover and what to leave underwater?
We work in collaboration with the Egyptian Ministry of Tourism and Antiquities and according to their policies. Although it very much depends upon the type of object that we find, in general, we are allowed to bring up and study much of the material that we excavate so that we can use them to give us new hints on how the ancient inhabitants of our sites lived, traded, built houses and ships and so on. Obviously, for significant artefacts, such as large elements of statuary, we usually recover them all for scientific study and possibly for future museum display (although there are exceptions, see below). Similarly, all of the coins that we find are carefully recovered for study. Other artefacts, such as pottery sherds, however, are much more numerous and so we need to be more selective. Our archaeological divers recover the diagnostic elements; rims, bases, and handles, along with any painted or otherwise decorated body sherds that might also provide important scientific information. These are all given to our team of ceramics experts. Finally, there are things like the large blocks of limestone or marble and granite columns that were used in the construction of the temples and other important buildings on the sites. For materials like this, we record them underwater and leave them where we found them. The exceptions here are for architectural elements that have inscriptions typically in hieroglyphs or in Greek.
Are there any objects from the site that are too big or eroded to bring to the surface?
Yes, in the Eastern harbour of Alexandria we have discovered and studied, statues, columns and other artifacts underwater and have left them in situ where we found them so that hopefully, in the future, they can be part of an underwater museum or perhaps even a dive trail. In Thonis-Heracleion the site is more open to the erosive actions of the sea and less suitable for an underwater museum and so we recover the important pieces of statuary that we have left in position in Alexandria. However, as noted above, even here somethings are definitely too big and eroded to bring to the surface and we leave the columns (some up to 6 m long), their capitals, and limestone blocks from the temples and other important buildings where we found them. There is also the issue of the wooden ships that we excavate and study in Thonis-Heracleion. Some of these are over 25 m long and 8 m wide and it would be a huge logistical and conservation effort to lift and then preserve these remains out of the water. Consequently, following our excavation and study, these ships and boats are carefully reburied. Although we have found over 70 ancient ships in Thonis-Heracleion, we have only excavated a few of them, each of them carefully selected to answer specific questions. For the majority, we just note their position, record what is visible, and then leave them for future generations of archaeologists to study.
How many dive hours have you logged on the project thus far?
In Egypt, during each mission we dive twice a day for around two to two and a half hours per dive, depending on what we are doing. The missions are approximately 45 days long and we dive seven days a week with a team of, on average, 14 archaeological divers. We have been working for 20 years and so multiplying all of this up gives a minimum of around 63,000 hours knowing that some years we have 2 missions per year, which could add to this total number.
Why did Thonis-Heracleion sink into the sea?
To answer this question, there are a combination of different geological and geomorphological process that need to be considered. Firstly, there is the issue that Thonis-Heracleion was built on loose sediments lain down by the river Nile in its Delta. Over time, these sediments compact and result in a slow rise in sea level and so temples that were built several metres above sea level, have waters lapping at their doors after a few hundred years. This resulted in the older parts of the site of Thonis-Heracleion being abandoned as its inhabitants moved to higher and dryer ground. In addition, there is also a second major process that needs to be taken into account: liquefaction. This is a localized phenomenon that can be triggered by the action of great pressure on soil with a high clay and water content. The pressure from large buildings, combined with an overload of weight due to an unusually high flood or a tidal wave, can dramatically compress the soil and force the expulsion of water contained within the structure of the clay. The clay quickly loses volume, which creates sudden subsidence. An earthquake can also cause such a phenomenon (ancient texts mention the disappearance of cities here through both earth tremors and tidal waves). These factors, whether occurring together or independently, may have caused significant destruction and explain the submergence of Thonis-Heracleion and Canopus.
Can you talk about the conditions underwater? Do you feel that the water temperature/salt level helped to preserve your findings?
Aboukir Bay isn’t the pristine diving paradise found on Egypt’s Red Sea coast for instance. For us, underwater visibility is sometimes measured in centimetres instead of the tens of metres found elsewhere in the Mediterranean. This is because of the shallow sandy seabed, the silt from the Nile, and the algae that live in its waters. Together these combine to make diving a little more challenging than elsewhere. Nevertheless, the waters are warm making it comfortable to dive in our red wetsuits; indeed, it’s very rare for us to get cold!
The submergence of our sites has helped to preserve them, particularly for sites like Thonis-Heracleion, where their catastrophic destruction stops the city at a moment in time as it is plunged into the waters. For a start, this removed the cities from the normal ongoing process of urban development where old buildings would be demolished, recycled, and replaced, as the ancient city slowly turns into a modern one. The murky waters have also helped to protect them from looting as often happens with archaeological remains on land. Furthermore, our sites are now covered with sand and sediments, sometimes up to several meters thick, that can protect them from erosion. We have objects, like the stele of Thonis-Heracleion, which are perfectly preserved. Its inscription looks like new, even though it is thousands of years old.
Why did it take until the 1990s for someone to actually find these submerged cities?
The names of the lost cities of Thonis, Heracleion, and Canopus were preserved in ancient history books, but when early archaeologists started to look for them, they only looked on land. For these early archaeologists it was inconceivable that a site could be found underwater several kilometres offshore. Our cities are also covered by several meters of sand and sediments and it is perfectly possible to dive down to the seabed and not know that you are swimming over the remains of an important ancient city. You can imagine that it was extremely difficult to find any traces before technical equipment was developed with which you could locate them. For instance, together with the French Atomic Energy Commission we developed the Nuclear Magnetic Resonance (NMR) Magnetometers for underwater archaeological research. These highly sensitive instruments create magnetic maps of the seabed, which can provide vital clues about the location, orientation and size of potential buried archaeological features. We started our co-operation with the Egyptian Ministry of Tourism and Antiquities in the 1990s and have continued our research until today.
With the objects you have already discovered, what questions are still unanswered?
We presume that we have only discovered five percent of the city of Thonis-Heracleion. There is so much more to discover and learn about the ancient city. When you think about Pompeii being explored since the 18th century and research is still not finished today, you can imagine that it will take much longer for Thonis-Heracleion, being twice the size of Pompeii and being underwater.
In addition to this, when we first started working at Thonis-Heracleion, for example, the questions that we could initially ask were quite simple: how big was the site, what did its major topographical features look like, what period did it date from and so on. As we’ve done more work and gathered much more evidence, the questions that we can ask have become increasingly complex and tell us interesting about life in the city. For example, we’ve discovered that the main area of settlement moved from the north of the site in the Pharaonic period to the Central Island in the Ptolemaic period. We’ve been able to think about why this happens and begin to understand the responses of the inhabitants of the city to their changing environment. For us, as archaeologists, new discoveries bring new knowledge, but they also lead to new questions; who knows where this will lead us!
Besides the discovered objects, what is there to learn from ancient civilizations?
Although it seems that our work is only about the past, this isn’t entirely true. In Thonis-Heracleion, for example, we are studying a city in which the effects of a slow rise in sea level are clearly seen, as are the responses of its inhabitants to this. For example, the movement of the main temples onto the Central Island was due to the flooding of parts of the northern city and was down to the resilience of the population and their determination to remain at this important sacred and strategic site.
Today, low lying cities are also facing a future where rising sea levels will threaten the ongoing viability of life in them. In a similar way, Thonis-Heracleion was a thriving port city at the sharp end of dealing with foreigners: raiders, traders, and immigrants. We can trace through time a reaction that was initially hostile and suspicious of Greeks, but one that grew through trust and the adoption and adaption of different artefacts and ideas, to finally the creation of a new blended society. Consequently, can our studies about environmental change and migration and integration offer a sense of historical perspective on these pressing issues in our contemporary world?