Coastal and Ancient Harbour Geoarchaeology

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© Blackwell Publishing Ltd, The Geologists’ Association & The Geological Society of London, Geology Today, Vol. 26, No. 1, January–February 2010

FeatureCoastal and ancient harbour geoarchaeology

N. Marriner1, C. Morhange1 & J.P. Goiran2

1CNRS CEREGE UMR 6635,

Université Aix-Marseille,

Europôle de l’Arbois, BP

80, 13545 Aix-en-Provence

Cedex 04, France.

[email protected] MOM Archéorient

UMR 5133, 5/7 rue Raulin,

69365 Lyon Cedex 07,

France.

What roles have human impacts and natural processes had in shaping the evolution of Mediterranean coastlines during the Holocene? Where, when and how did societies transform the coastal zone? At what scales and rhythms did these changes take place? What can ancient harbour sediments tell us about human-environment interactions? During the past 20 years, geoarchaeological research in the Mediterranean has attempted to understand the interplay between culture and nature, and more particularly how environments and processes have played a role in Holocene human occupation of the coastal zone. This approach has drawn on the multidisciplinary study of sediments, as archives of information, to attempt to differentiate between anthropogenic and natural factors, the latter, we argue, having played an increasingly secondary role with time. Three important spatial scales of analysis have emerged, local, regional and Mediterranean, all of which are outlined here.

Until relatively recently, coastal sediments uncovered during Mediterranean excavations solicited very lit-tle attention from archaeologists, even though the traditional view of Mediterranean history has placed emphasis on the influence of physical geography in fashioning the region’s societies. Prior to 1990, the relationships between Mediterranean populations and their coastal environments had largely been studied in a fragmentary manner, either from an anthropo-logical or naturalist standpoint, but rarely were the two married together. During the past two decades, Mediterranean archaeology has witnessed the emer-gence of a new culture–nature duality, drawing on the Anglo-Saxon examples of beach ridge and water-front archaeology. Indeed, archaeologists are today increasingly aware of the importance of the environ-ment in understanding the socio-economic and natu-ral frameworks in which ancient societies lived, and multidisciplinary dialogue has become a central pillar of most large-scale Mediterranean excavations.

Within this interpretative context, ancient har-bours have yielded particularly rich sedimentary archives, shedding new light on how humans have locally interacted with and modified the coastal zone since the Neolithic (Fig. 1). It is at the end of the Holocene marine transgression, around 6000 years ago, that societies started to settle along ‘present’ coastlines; since this time, ancient civilizations have

exploited a plethora of environmental contexts as an-chorages, from natural bays (e.g. up until the Middle Bronze Age) through to completely artificial basins during the Roman period. Whilst some of these port complexes continue to be thriving transport centres, many thousands of years after their foundation, oth-ers have been completely abandoned. Why? The un-derpinning principle follows that long-term human subsistence favoured access to the open sea and that coastal occupation sites have paralleled changes in the shoreline. Humans have therefore adopted adap-tive strategies to overcome the rapidly changing face of Mother Nature.

During the early 1990s, two large-scale urban excavations were undertaken at opposite ends of the Mediterranean. The studies were unique in that, for the first time in a Mediterranean coastal context, both looked to embrace a multidisciplinary methodology. Investigative fields included not only archaeology but also geology, geography, history and marine biology. The first, at Caesarea Maritima in Israel, investigated a completely artificial Roman harbour on the Levan-tine coast, active between the first and second centu-ries AD (Fig. 2). At Marseille, meanwhile, researchers set about reconstructing the archaeology and envi-ronmental evolution of the city’s ancient harbour, still known as the Vieux Port, following its founda-tion during the sixth century BC by Greek colonists

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from Ionia. Since this pioneering work there has been a great proliferation of studies looking into coastal and ancient harbour geoarchaeology. Seaport ba-sins are particularly interesting as they allow us to understand how people ‘engaged with’ and ‘adapted to’ local environmental processes. In this paper, we present a short overview of ancient harbour geol-ogy, the methods employed and the specific interest of harbour sediments in reconstructing ancient coastal landscapes and their evolution through time. We will consider three scales of analysis, local, regional and Mediterranean.

Local scale—palaeoenvironmental study of harbour basins

During the past 20 years, ancient harbours have attracted interest from both the archaeological and Earth science communities. In tandem with the development of rescue archaeology, and more spe-cifically large-scale urban excavations, the study of sedimentary archives has grown into a flourishing branch of archaeological inquiry. It has effectively been demonstrated that ancient harbours constitute outstanding archives of both the cultural and en-vironmental pasts. Their sediments are particularly rich in research objects (bioindicators, macrorests, artefacts, etc.), a multiplicity that accrues not only insights into the history of human occupation at a given site, but also the mobility of its coastlines, in addition to the natural processes and hazards having impacted these waterfront areas.

In geoarchaeological terms, what is an ancient harbour and why have they attracted interest from

environmental scientists? Ancient harbours are both natural and constructed landscapes, comprising three elements of note:1. The harbour basin. For an archaeologist, the harbour

basin is characterized by its artificial structures, such as quays, moles and sluice gates. Since the Bronze Age, there has been a great diversity in harbour infrastructure, from natural pocket beaches serving as proto-harbours in Bronze Age Levant, through the first Phoenician mole dated to around 1000 BC, to the grand offshore constructions of the Roman period rendered possible by the discovery of hydraulic concrete. Recent research has sought to characterize and date these different infilling phases by means of the unique sedimentary signature each technology brings about. In their study of harbour landscapes, geoscientists are also interested in two additional research objects, the sedimentary contents of the basin and relative sea-level changes.

2. Ancient harbour sediments. Port basins comprise unique base-level depocentres, for the most part constituting fine-grained sediments. Shifts in the granularity of these deposits translate the degree of harbour protection, often characterized by a rapid accumulation of silts following a sharp fall in water competence. For instance, accumulation rates of 20 mm/yr have been recorded in the Graeco-Roman harbour of Alexandria. High-resolution study of the bio- and lithostratigraphical fractions—obtained either by coring or through the study of sections—yields insights into the nature of ancient harbour-works. This new approach is complementary to results obtained during archaeological excavations in the coastal and hinterland valley areas. The anoxicity of harbour depositional contexts, linked to the high water table and fine-grained sediments, is particularly conducive to the preservation of perishable artefacts such as leather and wood.

3. The palaeo-water column. Nowadays, most ancient harbours are completely infilled. Using biological indicators fixed to quays, it is possible to identify and date former sea-level positions that, when compared with the marine bottom, allow the height of the palaeo-water column to be estimated. This information is critical in understanding the history of sedimentary accretion in addition to estimating the draught depth for ancient ships. These two reference levels, the palaeo-sea level and sediment bottom, are mobile as a function of different forcing parameters including tectonics, sediment budgets and human impacts such as dredging. They define the accommodation space invariably infilled with fine-grained sediment. In effect, the overriding problem posed by artificially protected harbours was the impact of acute sediment accumulation,

Fig. 1. Geoarchaeology of Mediterranean coastlines: a multidisciplinary approach.

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which could rapidly reduce the draught depths necessary in accommodating the largest ships. To counter this problem, ancient societies developed a number of different methods, including sluice channels and dredging of the marine bottom.

During the past 20 years, multidisciplinary inquiry has allowed a better understanding of where, when and how ancient Mediterranean harbours evolved. This is set within the wider context of a new ‘in-strumental’ or ‘quantitative revolution’ towards the environment.

Where? The geography of ancient harbours constitutes a dual investigation that considers not only the location but also the extension of the basins. When allied with a study of aerial photographs and satellite images, bio-stratigraphical analysis of sediments is a powerful tool in identifying coastal areas that could have served as ancient roadsteads. Figure 3, for example, shows a core drilled in the city centre of Tyre, adjacent to the present harbour. The ostracod assemblages attest to a well-sheltered port basin between the Hellenistic and Byzantine periods, today buried beneath the modern market by thick sediment tracts. Multiple sediment cores allowed us to propose a new cartography for the ancient northern harbour of Tyre and demonstrate that during antiquity it was approximately twice as large as present. This approach allows us to not only precisely reconstruct ancient shorelines (e.g., as at Sidon, Alexandria or Marseille), but also to relocate ports for which no

conspicuous archaeological evidence presently exists, such as at Cuma, in Italy.

When? Chronology is essential in understanding modifications in harbour technology and the timing of human impacts, such as lead pollution from the Bronze Age onwards, or ecological stresses translated by changes in faunal assemblages. The overarching aim is to write a ‘sedimentary’ history of anthropogenic coastal impacts and technologies, using quantitative geoscience tools and a standardized stratigraphical framework.

How? This is a fundamental question in ancient harbour geoarchaeology that can be investigated at a variety of spatial and temporal scales. It enables us to differentiate between direct impacts—for instance, environmental modification linked to the construction of a causeway, as at Alexandria and Tyre—from indirect impacts, such as human-induced erosion of watersheds. Recent results demonstrate that these impacts were relatively moderate during the Bronze Age whilst, by contrast, an apex of anthropogenically forced environmental degradation is attested during the Roman and Byzantine periods.

Regional scale—valley bottoms, rias and deltas

At base level, the coastline records changes in sedi-ment budgets. This micro-regional scale has long at-

Fig. 2. Location map of sites discussed in the text.

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tracted interest from geomorphologists as it enables the environmental processes in proximity to ancient cities to be characterized. The research objects consid-ered are for the most part geomorphological, includ-ing delta progradation, avulsion and ancient harbour abandonment linked to rapid shoreline changes. This approach, called ‘archaeological geology’, has long been used by Homeric archaeology looking to relocate ancient sites and reconstruct the evolution of their landscapes subsequent to the seminal nineteenth cen-tury work of Schliemann.

Around 6000 years ago, following a deceleration in post-glacial sea-level rise, Mediterranean coasts were characterized by an indented morphology con-sistent with the drowning of its seaboard valleys. Since this time, high sediment supply has led to the progradation of coastlines and a change in the con-comitant palaeo-environments from rocky coasts to deltaic or lagoonal environments. As a function of the accommodation space to be filled, and sediment supply from the hinterland, the rate of progradation has been variable. For instance, geological investiga-tions of the Menderes ria in Aegean Turkey, indicate that the delta has grown more than 18 km since mid-Holocene times.

In light of this, it is important to compare and contrast the hyper-sedimentation of ancient harbours with the history of erosion—be they climatic or hu-man induced—in Mediterranean watersheds. With-in this context, ria valley bottoms are particularly interesting. For instance, Devillers, working on the Gialias delta in Cyprus, has reconstructed a vast ma-rine bay that formed around 8000–6000 years ago following the drowning of the lower reaches of the Gialias palaeo-valley. Gradual deltaic growth led to the dislocation of four ancient harbour sites, Kalop-sida (Early/Middle Bronze Age), Enkomi (Middle/Late Bronze Age), Salamina (Graeco-Roman) and Fama-gusta (Medieval) as societies strived to adapt to the rapid coastal changes and maintain access routes to the open sea. In a similar vein, small islands, such as Malta (24 × 12 km), are particularly conducive to geoarchaeological studies as their reduced size allows both geomorphological and anthropogenic systems to be examined in their entirety, from source to sink.

Mediterranean scale

The multiplicity of sites investigated has brought to light a number of different patterns. We identify three areas, discussed below.

Geomorphological typology of ancient harbours In other papers, we have proposed a non-exhaustive geoarchaeological classification of ancient Mediterranean harbours, comprising seven different contexts. Drowned and uplifted harbours are the results

of neotectonic movements producing a rapid change in relative sea level, and hence the functionality of the former basins. The best examples include Puteoli (present day Pozzuoli), Alexandria (drowned) and Phalasarna (uplifted). Where relative sea-level changes have been relatively minor (e.g. < 2 m since 6000 years BP), sediment supply has been the key forcing agent in shaping the evolution and taphonomy of ancient roadsteads. Buried urban harbours (Byzantium/Istanbul, Marseille, Beirut, Tyre), landlocked harbours (Ephesus, Priene, Troy), buried lagoonal harbours (Cuma, Coppa Nevigata), and buried fluvial harbours (Aquileia, Rome, Portus Ostia, the Nile’s harbours) all fall into this latter category. Finally, in areas of low sediment supply, harbour infrastructures can be significantly eroded, such as Caesarea’s outer basin. This harbour type is generally found in high-energy contexts, away from major fluvial systems, and is generally attributed to the Roman period when the use of hydraulic concrete meant that natural roadsteads were no longer a prerequisite for seaport location. Other scholars have set out typologies for given chronological periods including most recently Carayon’s comprehensive geoarchaeological classification of ancient Phoenician and Punic harbours. It is hoped that future work will

Fig. 3. Ostracod assemblages of core TV from the ancient northern harbour of Tyre.

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further improve these groupings.

Sequence stratigraphy It is important to move beyond descriptive, locally specific stratigraphies in order to assimilate the conceptual framework offered by sequence stratigraphy. This holistic and deductive approach facilitates inter-site comparisons by insisting upon both processes and surface discontinuities, such as the maximum marine ingression (6000 years BP) or harbour foundation and abandonment surfaces. Significantly, sequence stratigraphy also integrates sea-level flooding surfaces, which allows sites in diverse geographical and environmental contexts to be compared and contrasted on the basis of the same reference level (Fig. 4).

Working typology of human impacts In order to propose a geological typology of coastal civilizations, it is important to move beyond individual case studies and propose correlations for different harbour types and chronological windows (Bronze Age proto-harbours, artificial Iron Age harbours, etc.). Ancient harbour sediments are particularly interesting as they allow specific environmental processes to be married with archaeological information. In terms of anthropogenic forcing agents, it is possible to discriminate seven major impacts, both at the scale of the ancient harbour and the coastal watershed.1. Granulometric impacts. The onset of harbour

infrastructure leads to a significant reduction in sediment grain size, arising from a sharp fall in water competence. In a general manner, transition from medium beach sands to silts and clays marks the beginning of a confined harbour basin (Fig. 4).

2. Watershed erosion crises and detritic impacts. A longstanding debate in Mediterranean geoarchaeology has been the notion of a ‘fall from Eden’, or more particularly the destruction of a ‘pristine’ landscape by humans. Traditionally, this theme has been studied using cut and fill landscape remnants in Mediterranean valleys, although in recent years the coastline has also attracted significant interest from geoarchaeologists as it acts as a terminal sink for the sediment conveyor. Since the beginning of the Christian era, geomorphological research in the western Mediterranean has identified three major erosion crises during the Augustan period (2000 years ago), late Antiquity and the Little Ice Age. These periods were characterised by pronounced coastal progradation induced by increased sediment fluxes from the tributary watersheds.

3. Geomorphological impacts. One of the direct consequences of this massive increase in sediment supply was a rapid accretion of human-modified coastlines. For example, at Tyre, the construction

of Alexander the Great’s causeway led to the rapid entrapment of fluvially-derived sediment to form a sand-spit, or tombolo, which segmented the original palaeo-bay in two and linked the former city island to the adjacent continent (Fig. 5).

4. Stratigraphical impacts. In terms of sequence stratigraphy, a new working terminology and interpretative framework that is applicable to ancient harbours has been proposed. Two surfaces of discontinuity have been identified, the Harbour Foundation Surface, which corresponds to the initial construction of harbour works, and the Harbour Abandonment Surface linked to a degradation or semi-abandonment of port infrastructure following the demise of its adjacent urban agglomeration.

5. Mineralogical impacts. In a semi-arid context, artificial harbour basins can lead to the neogenesis of minerals such as gypsum crystals (e.g. the Phoenician harbour of Kition Bamboula in Cyprus or Alexandria, Egypt). These precipitates translate hyper-saline conditions that are unfavourable to harbour activities over the medium to long term.

6. Biological impacts. Faunal assemblages translate the magnitude of ecological changes brought about by the transformation of a pocket beach to a semi-artificial lagoon. For example, at Alexandria, organic matter and upper muddy sand assemblages superseded sand loving biocenoses during the fourth century BC. In Lebanon’s ancient harbours,

Fig. 4. Stratigraphical model of ancient Mediterranean harbours and natural coastlines (adapted from Marriner & Morhange 2006).

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the technological apogee of Beirut, Sidon and Tyre’s seaports is characterised by the monospecific domination of Cyprideis torosa, a lagoonal ostracod species.

7. Geochemical impacts. Lead isotopes have been demonstrated to be particularly good proxies of human impacts, particularly metallurgy, since 5000 years BP. For example, sediments from Alexandria’s ancient harbour have been used to document metallurgic activities some 2000 years before the foundation of the city by Alexander the Great. Such evidence can therefore be used to resurrect debates on the foundation date of certain cities, in addition to comprehending the history of artisanal and industrial activities over the medium to long terms.

Conclusions

What role, if any, do palaeoenvironmental data have to play in policy and urban planning? In collabora-tion with local, regional, national and international political actors, we argue that geoarchaeology can also serve as an applied science. By studying coastal changes, it is not only possible to understand environ-mental evolution, but also more accurately pinpoint archaeological structures; this information can subse-quently be transmitted to urban planners and policy makers. A major problem facing the majority of coast-al archaeological sites, particularly ancient harbours, is their location at the heart of urban agglomerations. Recent examples in Beirut and Marseille demonstrate that the vast majority of potentially rich archaeologi-cal zones are destroyed during construction works.

In many instances a classic dig is unrealistic for both financial and logistical reasons, be it pressure from property developers, costs or presence of the water table. Within this context, a multidisciplinary geoar-chaeological approach can yield rapid results and aid planners in identifying and protecting the most im-portant archaeological zones for future protection.

Acknowledgements

We wish to thank ANR Paleomed and CNRS PEPS SHS (P09/0017) for financial support.

Suggestions for further reading

Abulafia, D. (ed.) 2005. The Mediterranean in History. Thames & Hudson, London.

Bini, M., Chelli, A., Durante, A. M., Gervasini, L. & Pappalardo, M. 2009. Geoarchaeological sea-level proxies from a silted up harbour: A case study of the Roman colony of Luni (northern Tyrrhe-nian Sea, Italy). Quaternary International, v.206, pp.147–157.

Braudel, F. 2002. The Mediterranean in the Ancient World. Penguin, London.

Brückner, H., Müllenhoff, M., Handl, M. & van der Borg, K. 2002. Holocene landscape evolution of the Büyük Menderes alluvial plain in the environs of Myous and Priene (Western Anatolia, Turkey). Zeitschrift für Geomorphologie, v.127, pp.47-65.

Butzer, K.W. 2008. Challenges for a cross-discipli-nary geoarchaeology: The intersection between environmental history and geomorphology. Geo-morphology, v.101, pp.402–411.

Fig. 5. Evolution of Tyre’s tombolo between the fourth century BC and today.

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Franco, L. 1996. Ancient Mediterranean harbours: a heritage to preserve. Ocean and Coastal Management, v.30, pp.115–151.

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Marriner, N. & Morhange, C. 2006. The Ancient Har-bour Parasequence: Anthropogenic forcing of the stratigraphic highstand record. Sedimentary Geol-ogy, v.186, pp.13–17.

Marriner, N. & Morhange, C. 2007. Geoscience of ancient Mediterranean harbours. Earth-Science Re-views, v.80, pp.137–194.

Marriner, N., Morhange, C. & Carayon, N. 2008. An-cient Tyre and its harbours: 5000 years of human-environment interactions. Journal of Archaeological Science, v.35, pp.1281–1310.

Morhange, C., Goiran, J.-P., Bourcier, M., Carbon-el, P., Le Campion, J., Rouchy, J.-M. & Yon, M. 2000. Recent Holocene paleo-environmental evo-lution and coastline changes of Kition, Larnaca, Cyprus, Mediterranean Sea. Marine Geology, v.26, pp.205–230.

Morhange, C., Blanc, F., Bourcier, M., Carbonel, P., Prone, A., Schmitt-Mercury, S., Vivent, D. & Hesnard, A. 2003. Bio-sedimentology of the late Holocene deposits of the ancient harbor of Mar-seilles (Southern France, Mediterranean sea). The Holocene, v.13, pp.593–604.

Rapp, G. & Hill, C. L. 1998. Geoarchaeology: The Earth-Science Approach to Archaeological Interpretation. Yale University Press, New Haven, CT.

Reinhardt, E.G., Patterson, R.T. & Schröder-Adams, C.J. 1994. Geoarchaeology of the ancient harbor site of Caesarea Maritima, Israel: Evidence from Sedimentology and Paleoecology of Benthic Fo-raminifera. Journal of Foraminiferal Research, v.24, pp.37–48.

Reinhardt, E.G., Goodman, B.N., Boyce, J.I., Lopez, G., van Hengstum, P., Rink, W.J., Mart, Y. & Ra-ban, A. 2006. The tsunami of 13 December AD 115 and the destruction of Herod the Great’s har-bor at Caesarea Maritima, Israel. Geology, v.34, pp.1061–1064.

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Coastal and Ancient Harbour Geoarchaeology