The BP exhibition

Sunken cities
Egypt’s lost
worlds

 

19 May – 27 November 2016

Supported by BP BP logo

Organised with the Hilti Foundation and
the Institut Européen d’Archéologie Sous-Marine

The BP exhibition

Sunken cities
Egypt’s lost worlds

19 May – 27 November 2016

Supported by BP BP logo

Organised with the Hilti Foundation and
the Institut Européen d’Archéologie Sous-Marine

Searching for sunken cities

Underwater archaeologist Franck Goddio is Director of the European Institute for Underwater Archaeology (IEASM). Here he tells us about the painstaking processes that lead to magical moments of discovery.

 

A detective story

At first, researching a site is rather like a detective story. For sunken cities, the first clues come from ancient texts that mention the existence of settlements that once stood near the coast. The next stage is to gather information on any past discoveries that could correspond with these sites. Sometimes a comparison of both sources can be productive – a town described as a thriving site many centuries ago may have eluded earlier archaeologists. If no trace of its existence has ever been discovered on land, could it have been covered by the sea? A geological study of the probable area can help – in the past, natural disasters have led to entire cities being lost under the sea.

The 110km2 area of survey. © Franck Goddio/IEASM.

Defining the survey area

Once we have determined the research area for a site, we carry out a methodical survey using the most sophisticated geophysical techniques available. This can take months, or even years. In the case of the cities featured in the exhibition – Thonis-Heracleion and Canopus – the preliminary survey lasted three years. Numerous electronic charts are generated from the data. We then make reconnaissance dives at promising locations.

Area of research, west of the Nile Delta (from Google Maps).

Making charts of the seabed

Searching for Thonis-Heracleion and Canopus in Abukir Bay, the huge size of the area prevented any systematic archaeological soundings, so we decided on a geophysical survey – using gravity, magnetic, electrical, and seismic methods. We first created a bathymetric chart – an accurate, measurable description and visual presentation of the seabed. This was done with an echosounder coupled with a differential global positioning system (DGPS), giving a depth accurate to 10cm and location accurate to one metre. The chart revealed a vast triangle of shallow bottom which seemed to correspond to probable sunken land. However, the area was still much too extensive for performing very high resolution surveys.

Bathymetric chart of the survey area. © Franck Goddio/IEASM.

Bathymetric chart of the eastern area. © Franck Goddio/IEASM.

Narrowing the search

We decided to perform a medium resolution magnetic coverage of this shallow area in order to select sub-area for very high resolution surveys. We used a highly sensitive nuclear magnetic resonance magnetometer developed for the IEASM by the French Centre for Atomic Energy. On the chart we could pinpoint various sub-areas of interest where the magnetic field appeared quite disturbed. One sub-area about 7km away from the present coast of Egypt showed important magnetic abnormalities.

Magnetic chart of the sub-area. © Franck Goddio/IEASM.

The beginnings of a discovery

We first surveyed this sub-area with a multi-beam echosounder coupled with a precision GPS. This rendered a 3D image of the seabed accurate to within one centimetre. This detailed bathymetric chart showed a remarkable underwater relief. On the east is a deep area bordered on its west by steep bumps. On the central part stands what could look like a peninsula in middle of depressions.

Multi-beams chart of the relief of the sea bed on a portion of the eastern sub-area. © Franck Goddio/IEASM.

Layers of sediment

We then performed what is known as a sub-bottom profiler survey. This produces images of the layers of sediment under the seabed. They revealed a zone of disturbed and sloping strata. To the east was a characteristic sedimentation pattern corresponding to an ancient river bed – the Nile. We confirmed these findings with soil coring – taking samples of the soil and testing them.

Data from the sub-bottom profiler. © Franck Goddio/IEASM.

Archaeological excavation

We decided to do a trial archaeological excavation in order to investigate a very strong magnetic abnormality. It was performed perpendicular to the magnetic abnormality in steps of two metres until we reached a hard clay bottom.

The locations of the various identification excavations on the large magnetic abnormality. Franck Goddio. © Franck Goddio/IEASM.

Numerous artefacts

The profile of the sediment strata revealed a channel that was three metres deep and 30 metres wide, filled with sediments in layers. Those layers yielded numerous artefacts such as ceramics, bronze coins, some gold jewellery, big lead containers and also some antique anchors. The lowest layer dates back to the 5th century BC and the highest to the 2nd century BC.

The underwater archaeological excavation. Photo: Christoph Gerigk. © Franck Goddio/Hilti Foundation.

An ancient channel

Along with the excavation, we performed a systematic reconnaissance of the surroundings where we spotted many ancient anchors. We hypothesised that the whole 300-metre-long magnetic abnormality could correspond to an ancient channel. We confirmed this with a second archaeological excavation 70 metres east. Four other very limited excavations were sufficient to determine the contours of the entire channel.

Schematic survey system. © Franck Goddio/IEASM.

Archaeological approach

Any excavation disturbs a site, so during any operation it is crucial to record all the data that the most up-to-date science and technology can gather. Underwater archaeology uses the same techniques as dry-land archaeology alongside skills that are specific to the marine environment. The taking of different kinds of samples, the study of the remains of monuments, buildings and boat hulls, the recording of the relative positions of the artefacts within the site – all of these require meticulous care. We begin conservation as soon as artefacts are brought to the surface, but this is just the beginning of a long process of preservation, restoration, recording and systematic study. We then publish the results in journals or books.

A multidisciplinary team

An underwater archaeological excavation demands many skills. It’s important to set up a multidisciplinary team, including archaeologists, historians, geophysical engineers, experts in restoration and conservation, divers who specialise in archaeological work, photographers, filmmakers and sailors. Gathering such a diverse group of people from different backgrounds to work underwater and live on board a boat together, sometimes for months, requires major organisational and logistical efforts. But in the end, it’s all worth it!

 

More about Franck’s work 

More about the Oxford Centre for Maritime Archaeology 

Membership

See the exhibition free as a Member

Tickets

Adults £16.50, under 16s free