Paleogeographic dynamics of the Ambracian Gulf

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Strongyli is situated at the northern extremity of Mavrovouni, atop a low ridge within an extensive wetland system, much of which is today drained. Understanding its spatial position is closely linked to the examination of the long-term changes in the Ambracian Gulf coastline, phases of marine transgression and regression during the Holocene, and the successive shifts of the Louros River course, a river that played a decisive role in shaping the western sector of the coastal plain. Around the mid-5th millennium BCE, the sea penetrated much further north than its present position, transforming isolated hills such as Mavrovouni into islets within the Ambracian Gulf. At that time, Strongyli was immediately adjacent to a coastal environment; from approximately 4500 to 3600 BCE, shallow marine or coastal conditions prevailed, with the site being directly coastal or even forming a small promontory surrounded by brackish waters. After the end of the maximum hydrostatic rise (c. 1500 BCE), the coastline gradually retreated southward due to significant sediment deposition. This process was primarily driven by fluvial input from the Louros River, which temporarily stabilized along a southern or south-western course, delivering fine sediments to earlier marine basins and converting them into extensive wetlands and, later, deltaic lands. Strongyli, located on a natural elevation, remained throughout this transitional phase at the interface of land and water, controlling a pivotal space where riverine and marine processes created exceptionally rich and productive microenvironments.

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The Louros was the principal agent shaping the western Ambracian plain. Evidence indicates that in antiquity its course did not follow the present-day western diversion but flowed more directly south, possibly discharging either directly into the Gulf or into the Tsoukalio lagoon. The older riverbed, prior to modifications between the 10th and 15th centuries CE, lay much closer to Strongyli than today. Sediment analysis shows that the area was significantly influenced by riverine deposition, confirming the proximity of an active Louros channel during Roman times. From 1500 BCE to the Middle Ages, the coastline progressively receded, the landscape became increasingly marshy, and the gradually shifting Louros channel created new strips of fertile land. Strongyli transformed into a location dominated by wetland conditions, though no longer directly coastal. This geomorphological evolution explains the persistence of occupation at the site into the late Byzantine and Ottoman periods. The river’s eventual shift to its present course—occurring between the 10th and 15th centuries CE and likely engineered to drain marshes and expand arable land—moved the Louros westward, rendering Strongyli more distant from the riverbed, yet still embedded within a lacustrine-wetland environment. During the Roman period, Strongyli occupied a coastal position very near an extensive seafront. The presence of the Roman villa rustica at this time was likely linked to exploitation of the land and shoreline. Proximity to the sea and brackish deposits ensured access, productive resources, and avenues for trade. Therefore, Strongyli’s location—always straddling wet and dry zones, near but never far from riverine and maritime resources—appears to have conferred enduring functional significance. In prehistory, access to rich aquatic ecosystems facilitated settlement. In historical periods, proximity to the Louros River and the Ambracian Gulf provided opportunities for transport, exploitation of natural resources, and agricultural production within a fertile but demanding environment. In the Middle Ages, control over wetland areas, even as the coastline receded, continued to offer geostrategic value through arable land and water collection.

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In conclusion, the paleogeographic formation of the Ambracian Gulf exemplifies a dynamic coastal environment where the interaction of marine and fluvial processes shaped both the natural landscape and human settlement. Throughout prehistory and history, the region formed a shifting mosaic of lagoons, estuarine systems, fluvial deposits, and coastal natural boundaries. The enclosed morphology of the Gulf, coupled with intense sediment deposition by the Arachthos and Louros rivers, progressively shifted the coastline southward, fundamentally altering the land-sea interface and decisively affecting the character and function of coastal settlements. The Arachthos and Louros were the primary agents of accretion, creating extensive alluvial fans that gradually filled the northern sectors of the Gulf. In the prehistoric period, large parts of the modern plain were shallow marine or lagoonal zones. Around the 3rd millennium BCE, the Rogoi area (Vouchetio) appears to have been a coastal islet or promontory. Between the Classical and Roman periods, sedimentation intensified, linked both to natural flood phases and to deforestation and agricultural activity in the hinterland. This transformation gradually converted open marine waters into marshes, brackish lagoons, and eventually terrestrial areas. In this context, Castle Rogoi occupied a critical position. Its siting on a natural elevation controlling the Louros estuary reflects the need to oversee maritime and terrestrial networks. At the time of its founding and peak, the site had direct access to maritime routes, facilitating trade and military oversight. However, with progressive sedimentation and coastal retreat, Rogoi shifted inland, losing its initial strategic role.

Similarly, Strongyli, built on a low elevation, was situated in an environment highly exposed to wetland dynamics. Its proximity to lagoonal systems and brackish zones likely explains the presence of economic activities related to agriculture, livestock, and exploitation of aquatic resources. Frequent flooding, sediment deposition, and hydrological changes directly affected settlement and site occupation. Unlike Rogoi, Strongyli’s significance did not rely on strategic oversight but on access to wetland resources, representing a characteristic form of settlement in a dynamic coastal environment. Comparative study of the two sites reveals distinct modes of adaptation to the same changing landscape: Rogoi reflects the defensive-administrative role of a control node within a coastal network, while Strongyli exemplifies the economic-exploitative function of a wetland system. In both cases, paleogeographic evolution was a decisive factor in the prosperity, function, and abandonment of these sites. Prehistoric, Classical, Hellenistic, and Roman periods in the Ambracian Gulf cannot be understood without a close integration of geomorphology, hydrology, and human activity. Strongyli and Rogoi, as complementary examples of coastal space utilization, illustrate the inseparable link between natural processes and human settlement choices.

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The archaeological landscape of Old Epirus in Late Antiquity and the Early Byzantine period was organized into a system of central and peripheral sites around the Ambracian Gulf. Nicopolis, as a product of Roman political initiative and later a metropolitan capital, functioned as a lever of urbanization and spatial management. The monumental character of public buildings, fortifications, basilicas, and documented administrative continuity reflect the city’s political, economic, and ecclesiastical significance. In contrast, sites such as Strongyli represent the other end of this system: small-scale rural and coastal establishments, architecturally functional and connected to the extraction and circulation of resources. The two locations, rather than being interpreted in isolation, constitute interdependent components of the same archaeological organism. Economy, settlement, exchange, and transport formed a unified network. Old Epirus, therefore, does not appear as a dispersed mosaic of unrelated settlements but as a hierarchical network in which the center (Nicopolis) ensured administration, control, storage, and ideological legitimacy, while the periphery (Strongyli and comparable sites) produced, supplied, and maintained the flow of resources and life. This model aligns with analogous structures in Late Antiquity across Greece and the Balkans, confirming that the study of smaller sites is not peripheral but essential for understanding the function of major urban centers. According to D. Drakoulis, the settlement, classified within the secondary network of Early Byzantine sites, as a Roman settlement of third-order size, located on the plain and by the river, controlled the productive resources of the adjacent lagoon.