1.1. Study context

The study of archaeological sites in their geological context is important to understand their urban development. Water sources are considered the primary limiting factor in the founding of cities [Crouch 2004, 1993], alongside agricultural potential and strategic positioning for defence, access and trade, rather than stone resources. However, local geology has inherent consequences for the raw materials available for construction throughout the history of a site. High-quality building stone can be regarded as a valuable factor essential for proper urban development and could have dictated the choices made by ancient builders: the need to import specific stones, the position of an edifice relative to the topography and the adaptation of construction and architecture to the specific properties of local stone. In fact, it has been observed that building material diversity captures geological resource diversity, and monument studies have shown regional trends in Greek architecture [Martin 1965].

Typically, geological investigations focus only on building materials inside archaeological sites, as seen at Delphi [de Vals et al. 2020], Epidaurus [Varti-Matarangas and Matarangas 2000] and Malia [Dimou et al. 2000]. Accordingly, few studies have been published regarding building material origins in relation to local geology; this has resulted in the lack of a comprehensive understanding of stone trades and uses, with the exception of the marble trade [Al-Bashaireh 2021, and references within]. Provenance studies tend to focus on allochthonous rocks but ignore local stones, yet local stones seem to represent the vast majority of stones employed in masonry. However, each site has a unique history and geological setting: accordingly, the main difficulty is in obtaining general patterns or overall trends, if they exist. In this study, we selected four sites within the same geological setting to allow comparative study. Our goal was to quantify stone diversity in archaeological buildings. Accordingly, this is not a detailed report of stone mechanical behaviour and construction techniques, although this topic would be suitable for further study.

Four major archaeological sites are located in the south-eastern part of the Gulf of Corinth: the Heraeum at Perachora, the sanctuary of Poseidon at Isthmia, the old city of Corinth and ancient Sikyon. The last three lie south of the Corinth Canal, whereas the Heraeum lies at the tip of the Perachora Peninsula. Sikyon, Corinth and the Heraeum open into the Gulf of Lechaion, whereas Isthmia opens into the Saronic Gulf (Figure 1). Sikyon is an independent city-state, but whether the sanctuaries of Perachora and Isthmia are part of the territory of the Corinth city-state remains the subject of debate [Wiseman 1978].

The study focusses on Archaic to Hellenistic ashlar masonry—finely dressed cut stones, as opposed to rubble masonry, between the 7th and the 1st centuries BC. We exclude sculptures and other building materials such as wood or tile. Marbles are used for construction if available locally in large quantities, for example in the Cycladic islands or in Attica [Martin 1965], but they do not crop out in the Corinth area. Here, they will be referred to as allochthonous stones and their provenance will not be discussed, because it is a complex issue [Vettor et al. 2021]: macroscopic descriptions are not sufficient to differentiate white marbles and thorough analyses with destructive sampling techniques are required. We will focus on limestones, specifically on the facies called “pôros” in modern literature, a term that we will not use because of its lack of geological meaning. For dates, we have adopted the conventional nomenclature BC (Before Christ) and AD (Anno Domini).

In this paper, stone provenance will be addressed using three specific terms: local, regional and allochthonous. “Local” lithologies are those found within the archaeological site or in its close vicinity, usually less than 1 km away. Local stones would have been produced primarily by earthworks, employed directly for construction, and thus did not require transportation. Stones are termed “regional” when they have been sourced from a broader area, from a few kilometres to several dozens of kilometres, which suggests precise selection criteria (prestige, quality of stones and other criteria yet to be defined). Stones are termed “allochthonous” when they have been quarried from facies at considerable distance from the site: up to hundreds of kilometres and, in our case, outside the Gulf of Corinth. Our provenance label is thus linked to the city where the stone was used: the Corinthian oolitic grainstone is considered a regional stone in Sikyon, but a local stone in Corinth.

Finally, the history of each site goes back to Mycenaean times at least, as indicated by antique literary sources. This study focuses on the Archaic to Hellenistic period, when the city-state model was mature: our goal is to explore the link between geology and construction during this period, from a materials perspective. We summed up geological observations inside and outside the archaeological sites and examined the integration of the sites with local topography. This background work will allow us to identify possible recurrent patterns in building materials and bring a new perspective on ancient Greek construction.

1.2. Geological setting

The Gulf of Corinth is a late Miocene–Quaternary rift that separates the Peloponnesus from Central Greece and results from the migration of the eastern Mediterranean subduction zone and the propagation of the North Anatolian Fault (NAF) [Armijo et al. 1996; Le Pichon and Angelier 1979; Moretti et al. 2003; Papanikolaou and Royden 2007] (Figure 1). The rift trends roughly E–W with a N–S opening, and cuts the formal Hellenides thrust, which is separated into the Internal and External Hellenides and oriented ca. N160. The rift is bounded by numerous normal faults cutting through the mainly Mesozoic carbonate basement and the first syn-rift deposits.

The Peloponnesus, and so the southern rift margin, has been subject to uplift since 1 Ma, whereas the northern margin has been sinking [Bell et al. 2009; Collier et al. 1992; Moretti et al. 2003; Rohais and Moretti 2017]. The eastern part, in the Isthmus region, is cut by major normal faults: the South Alkyonides Fault System (SAFS), the Loutraki Fault (LF) to the north and the Kenchreai Fault (KF) to the south [Papanikolaou et al. 2015] (Figure 2).

The global uplift of the Peloponnesus and the Isthmus has led to the exposure of complex syn-rift sedimentary units. These units record all water-level variations in the history of the Gulf of Corinth and are divided into three groups based on the syn-rift deposit classification [Rohais and Moretti 2017, and references within]: the Lower Group (5.3–3.0 Ma), Middle Group (3.0–0.8 Ma) and Upper Group (<0.8 Ma) (Figure 2). The Gulf was a set of lakes at the initiation of rifting, with mainly lacustrine and alluvial deposits at the base of the syn-rift series. The Middle Group deposits indicate a deepening of the depositional environment, with Gilbert-type fan deltas, distal turbidites and the deep marine facies further east. The Upper Group represents a major marine regression.

Two Upper Group formations are of particular interest here: a stepped marine terrace system in the region of Corinth up to Xylokastro, and beach-to-shoreface sequences cut by a horst-and-graben system in the Isthmus area [Armijo et al. 1996; Collier 1990, 1988; Collier and Thompson 1991; Papanikolaou et al. 2015; Sébrier 1977; vonFreyberg 1973]. The Perachora Peninsula also underwent regional uplift through the tectonic activity of the SAFS, leading to the formation of Pleistocene marine–shoreline deposits [Andrews et al. 2007; Dia et al. 1997; Leeder et al. 2008, 2005; Robertson et al. 2020] (Figure 2).

Each marine terrace is attributed to a Pleistocene sea-level highstand [Armijo et al. 1996; Imbrie et al. 1984]: six terraces in the Corinth area, splitting into eight terraces around Sikyon and ten further west, have been documented [Armijo et al. 1996; Dufaure and Zamanis 1979; Sébrier 1977]. The Laliotis (T2) and Sataka (T5) terraces are missing at Old Corinth, and younger terraces are more extensive north of Sikyon, near Xylokastro (up to ten). The Temple (T3) and Old Corinth (T4) terraces are the largest and most continuous: they can be followed from Corinth to Sikyon (Figure 2). This configuration gives the region the appearance of a large, flat amphitheatre, with a slight slope northward, incised by river valleys and opening up to the Gulf of Lechaios.

The terraces are composed primarily of conglomerates that unconformably overlie the “Corinthian Marls” [vonFreyberg 1973], which correspond to turbidites of the Lower and/or Middle Group, the latter of which is missing in the Isthmus area. However, the term “Corinthian marl” is often used without absolute dating in the literature and refers to unconsolidated units underlying the hard terraces. Over the Temple Terrace (T3) and the Isthmia sediment infill, oolitic tidal shoal formations, transverse dunes and longitudinal dunes are also present; the one near Examilia has been dated at 0.2 Ma and was quarried extensively in antiquity [Collier 1990; Collier et al. 1992] (Figure 2).

The terrace system does not extend to the Isthmus plateau, but the transition to other systems is unclear: the formations south of Loutraki could be linked to the New Corinth Terrace (6) [Collier and Dart 1991]. The Upper Group is composed of six transgressive–regressive cycles with erosive bases, defined onshore through the Corinth Canal and offshore thanks to recent core samplings [Collier 1990; Lykousis et al. 2007]. The Isthmia Graben is bounded by the Kalamaki–Isthmia Fault (KIF) to the north and by the Tamaris Fault (TF) to the south [Collier and Dart 1991; Papanikolaou et al. 2015].

The Holocene to Quaternary uplift of the Perachora Peninsula exposed marine–shoreline deposits. These are characterised by large microbial bioherms on the northwest shoreline of the peninsula’s tip [Kershaw and Guo 2006, 2003; Portman et al. 2005].

2.1. Site selection

The site selection was based on historical, material and geological factors.

All four sites were active from the Archaic to Hellenistic periods. We excluded the pre-Archaic and Roman periods because of major differences in construction techniques and materials. It seems that wood prevailed before the 7th century BC, and the Romans used different building materials, mainly bricks and a large variety of stones from the Mediterranean Sea [Martin 1965; Orlandos 1968]. The Corinthian area had also undergone pronounced urban development by the end of the 7th century, with city wall construction in Corinth and temple construction in Corinth, Isthmia and perhaps Perachora [Wiseman 1978]. Thus, ashlar masonry is particularly relevant in the time span chosen. Furthermore, quarrying techniques did not change significantly over the time period considered here; the Corinthian region is well known for its building material industry, including stones, and many quarry centres have been identified [Fant 2009; Hayward 2003; Wiseman 1978].

Three of the sites include all the public buildings that are considered to characterise a city: a stoa (a portico), a theatre, a stadium, at least one temple and enough remains conserved for the study to be relevant. We focused on these monuments because houses and common buildings were built with wood and rubble. Previous authors have observed that stones were restricted to large public infrastructure and suggested that allochthonous facies, like marbles, were imported for temples only [Martin 1965; Wycherley 1976] (see Figure 1 for the different temples present on each site).

Finally, these sites are all located in a similar environment, on the recent geological formations of the Corinth Rift. This point is crucial for determining recurrent patterns. However, although the geology is comparable at a regional scale, the local environments exhibit fundamental differences, in terms of both the exact lithologies available and geomorphological conditions. Moreover, the sites are close enough to have allowed exchanges of technology and building knowledge; thus, we anticipate that the main material differences between the sites should be due to their geology, rather than their historical development.

2.2. Inside and outside the archaeological sites

The building material inventory within each site is limited to macroscopic observations: however, each site has been visited multiples times and the nature of the studied stones meant that macroscopic descriptions were sufficient to distinguish between different facies. For architectural parts and other inaccessible remains (e.g. those destroyed or stored in museums), we relied mostly on previous works (archaeological reports, monographs and previous articles). The material descriptions are based on the classic criteria of sedimentary rock classification: grain size and shape, matrix characteristics, fossil assemblages and sedimentary structures present. The distribution in percentage of facies employed is based on our personal observations of the actual remains conserved. These percentages are estimated very approximately and represent only the very first step of a quantitative study of building materials; accordingly, they are intended to be adjusted subsequently. Nevertheless, these calculations will allow us to determine the dominant or marginal facies used in construction based on numerical evidence.

Each archaeological site was studied separately for the sake of clarity. This choice originated from the quantitative approach applied in our survey (facies identification, percentage and number of facies). Site specificities are considered in the discussion to qualify our numerical results: that Corinth and Sikyon are city-states, whereas Isthmia and Perachora are sanctuaries under Corinthian influence.

The geological survey was conducted during field campaigns in 2019 and 2020. For each locality, the study focused on the lithologies available around the site, their accessibility and the characteristics of the local building stone resource. Cross-sections show the relationship between the remains and the environment, and sampling of natural outcrops allowed basic laboratory work to be undertaken. Thin sections were made at Sorbonne University, and density measurements were performed using the triple weighing method.

2.3. Limits of the study

The results are limited by the vestiges’ quality, access and conservation, as well as the complex history of each site. Most remains are Roman and post-Roman in Corinth and Isthmia: Corinth was sacked by the Romans in 146 BC, and the sanctuary of Poseidon was abandoned for two centuries with the transfer of the Isthmian Games to Sikyon. The Archaic Temple of Isthmia was burned down and replaced by the Classical temple (with a marble roof), which was damaged by fire again in 394 BC. Moreover, most building stones used for this Classical temple and the wider site were re-employed for the Hexamilion Wall, a Roman fortification built from the 5th century AD to close the Isthmus [Gebhard and Gregory 2015]. The city of Sikyon was destroyed in 303 BC by a Macedonian general and rebuilt uphill, on the current site [Lolos and Koskinas 2011]: only predominantly Hellenistic remains are now available. The Perachora sanctuary was presumably abandoned around the 4th century AD and no modern city developed above it [Lefèvre-Novaro 2000]).

All of the post-Greek modifications have introduced bias into the data corresponding to Greek times: missing facies, repurposed building stone (or spolia) for new constructions and mistakes in the identification of Greek remains. Thus, only the verified Archaic to Hellenistic remains were studied: that is, buildings that are unanimously considered to be from these periods by the academic community. Pre-Archaic monuments and clearly Roman monuments, as well as Roman renovation work, were excluded.

3.1. The old city of Corinth

3.1.1. Topographic position and geomorphology

The site is located on Neogene to Quaternary sediments of the Peloponnesus, southwest of modern Corinth (Figure 2). The Mesozoic limestone basement composes the Acrocorinth, 1 km southward, but no older, magmatic or metamorphic units outcrop in the vicinity of the site. This means that there was no direct access to marble, granite or gneiss, but only to all of the lithologies of the syn-rift series: conglomerates, sandstones and marls from fine to very coarse, of fluvial to deep marine origin [Bornovas et al. 1972].

The site extends 2 km south of the current coast, and lies on two marine terraces initially defined by Sébrier [1977]: the Temple Terrace (T3) (ca. 240 ka) and the Old Corinth Terrace (T4) (ca. 210 ka) (Figures 2 and 3, map). The limit between the two terraces is poorly documented: the modern city extends all around the archaeological site, leaving few natural and accessible outcrops, and eluvial deposits cover the terraces. The main part of the archaeological site is located on the Temple Terrace (T3), but the gymnasium and the Asklepieion, with Lerna’s Spring, lie on the edge of the Old Corinth Terrace (T4) around 500 m northward (Figure 3, cross-section). The theatre, the first phase of which dates back to the 5th century BC, is built on the 30 m drop between the two terraces: the ancient Greeks took advantage of the difference in level to install bleacher seating. All these monuments, and most of the site, were used in the Roman period, when they were enlarged considerably [Sanders et al. 2018]. The Doric Temple of Apollo, ca. 23 m wide and 53 m long, seems deliberately built on the highest point of the archaeological site, and its foundations were carved directly out of the substratum (Figure 3a). It is one of the oldest monuments in the site, built in the 6th century BC, and the city developed around this natural hill as indicated by the implantation of Hellenistic and Roman monuments on its sides (Figure 3c) [Andrikou 2019].

3.2. Ancient Sikyon

3.2.1. Topographic position and geomorphology

The site of Sikyon lays south of the modern village of Vasiliko, on the western part of the uplifted marine terraces (Figure 2). No volcanic or metamorphic units are present, and the pre-rift limestone basement does not outcrop in the vicinity of the site (the Acrocorinth is more than 20 km to the south). The Neogene to Quaternary recent deposits of the Middle and Upper groups [Rohais and Moretti 2017] are directly available and include the conglomerates and marls of the Middle Group, conglomerates of the Pleistocene terraces and recent alluvial deposits. Occasional units of sandstones and sedimentary travertine can be found outside the limits of the plateau [Koutsouveli et al. 1989; Tataris et al. 1970].

The plateau of Sikyon lies around 20 km west of Corinth and 5 km inland, surrounded by the Asopos and Helison valleys. It corresponds to three marine terraces, as defined by Sébrier [1977], from south to north broadly as follows: the Laliotis Terrace (2) (ca. 350 ka), the Temple Terrace (3) (ca. 240 ka) and the Old Corinth Terrace (4) (ca. 210 ka) (Figure 4, map). However, the vestiges are concentrated on the third terrace, even though the remains of the city wall can be found throughout the plateau. The theatre and the stadium take advantage of the large level difference between the Temple and Old Corinth terraces [Hayward and Lolos 2015] (Figure 4, cross-section).

The vestiges correspond to the ancient acropolis, where the main buildings were excavated: a temple (perhaps dedicated to Apollo), ca. 11 m wide and 37 m long, built at the beginning of the Hellenistic period; a 106-m-long stoa or portico; a two-level palaestra, which occupied ca. 4500 m²; a 41 m² bouleuterion (a council house); one of the largest theatres of the Hellenistic period; and the stadium of ca. 200 m long [Lolos 2016].

3.3. The sanctuary of Poseidon at Isthmia

3.3.2. Sedimentary description and materials available

The site is located on the Upper Group formation of the syn-rift infill, composed of marine sequences, more precisely on a transgressive unit of beach-to-shoreface conglomerate and sand with an erosive base, unconformably overlying the marls of the Middle Group (Figure 5, cross-section) [Collier 1990; Rohais and Moretti 2017]. This unit exhibits large facies variability in both space and time. It corresponds to coarse-to-fine conglomerates, comprising 50–80% rounded centimetre- to millimetre-scale pebbles of primarily crystalline limestones and red radiolarites, with few quartzites. Accurate density measurements of such heterogeneous facies can be difficult to achieve, because their density depends on the proportion of limestone clasts (ca. 2.7 g/cm³).

Small marine units have been documented here: they crop out 300 m west of Kyra Vrysi, in the extension of the Liopesi Fault, and correspond to a marine detrital conglomerate with bivalves and perforated pebbles underlying the polymictic conglomerates. Within Lepes Gully, a fossil-rich marine laminated and heavily bioturbated sandstone underlies the 2-m-thick conglomerates. South of the late stadium, a finer layered polymictic conglomerate with a calcareous matrix of small oolites crops out (Figure 5b). On the Rachi Hill, a restricted unit of dune facies overlies a coarse conglomeratic unit. It is an oolitic grainstone with few fine conglomeratic units, and planar and cross-stratifications are visible. It extends towards the northwest and is not observed elsewhere around the site, but is similar to the grainstones observed at Corinth, Examilia and Kenchreai. No samples were obtained from the Rachi dune, but we consider its density to be similar to that of the oolitic dune of Examilia, i.e. around 1.6 g/cm³.

The conglomerates and oolitic grainstone from the Rachi Hill form thick homogeneous units that could be exploited for building materials. The other marine facies are too heterogeneous (in both nature and dimensions) and a small man-made cross-section, near the temple, illustrates the strong variability of this sequence (Figure 5c).

3.4. The Heraeum at Perachora

3.4.1. Topographic position and geomorphology

The Heraeum is located at the tip of the Perachora Peninsula, on a natural bay looking southward to the Gulf of Lechaios. The coasts of Perachora and Corinth are approximately 10 km apart (Figure 2). The sanctuary sits on Quaternary deposits that cover the Mesozoic limestone basement. Sandstones, marls, stromatolites and limestones are directly accessible and flysch, schist and ophiolitic formations outcrop a short distance away within the peninsula, but no magmatic units or marbles are present [Bornovas 1984].

The SAFS, along with sea-level variations, influenced the morphology of the western tip of the peninsula (Figure 2). Many active E–W oriented normal faults cut the limestone basement and recent formations; freshwater leakages along these faults caused stromatolite growth. The flat surfaces here are wave-cut platforms resulting from the sea-level variations [Robertson et al. 2020].

The lower sanctuary is located on the hanging wall of a major normal fault dipping southward, with the Doric Temple of Hera Akraia, built in the 6th century BC, having dimensions of ca. 10 m (width) and 30 m (length); a 4th century BC altar and L-shaped stoa are located east of the temple. The upper part lies on colluvium filling a fault-induced slump, including the Temple of Hera Limenia, which may also date from the 6th century BC, and a 35-m-long double-apsidal cistern (Figure 6, map) [Payne 1940]. The city associated with the sanctuary lies on the upper plain, approximately 500 m eastward and 50 m uphill, where an elaborate hydraulic system with monumental cisterns was dug into the ground (colluvium and recent sediments) [Tomlinson 1969].

4.1. Predominance of local high-porosity/low-density calcareous stones

Ancient Greek builders prized local sedimentary stones for their public infrastructure: conglomerates in Sikyon and Isthmia, oolitic grainstone in Corinth, stromatolite in Perachora. These stones comprise more than 80% of the volume employed at each site. The economic criterion seems to dominate the choice of building material: local stones require no transport, and blocks produced by earthworks can be used directly in construction. The few archaeological sources available regarding stone costs, particularly the construction accounts for Delphi, Delos and Epidaurus, suggest that the stone itself had no real price [Mathé 2010], and that the transport, cutting and laying of blocks dominated the overall cost of imported stones. We hypothesise that, by using local stones, stone costs would have been reduced significantly.

Additionally, geotechnical characteristics may have had some influence. The lithologies studied are usually called “pôros” in both modern and ancient literature: this refers to recent consolidated sediments with medium to low density, usually of light colour and easy to work with. Generally, it does not include conglomerates, although the finer conglomerate facies (in terms of granulometry) are sometimes referred to as pôros. High-porosity calcareous facies seem to have been sought after, like the calcarenite of Sikyon and the finer conglomerates of Isthmia; this is clearly illustrated by the oolitic grainstone facies that was exploited and exported widely. It can be observed in other regions: in Thessaly, at Volos, travertine from 6 km away [Vaxevanopoulos et al. 2015] and oolitic limestones from 70 km away [Melfos et al. 2016] were imported for construction.

Although used extensively, conglomerates do not meet all of the criteria for a good building stone [Bessac and Sablayrolles 2002]: they are heterogeneous and not particularly light, difficult and hazardous to cut and extract, inadequate for the finest architectural parts and subject to weathering. This is another argument for a primarily economic reason behind the choice of building material, as conglomerates were only used in the Corinth area when outcropping. A local breccia with similar properties was also employed in Delphi [de Vals et al. 2020]. However, conglomerates were not employed when an alternative existed, like the oolitic grainstone at Corinth.

In Sikyon and Isthmia, hard limestones are not directly available, but they outcrop at Perachora and in the vicinity of Corinth. However, they were not employed at all for ashlar masonry in any of the studied sites: this suggests that stone hardness was not a highly ranked criterion. The weight criterion seems more conclusive in the choice of building material: hard limestones were employed only when directly available and if no other less dense stones were present, in Delphi [de Vals et al. 2020] or in Epidaurus [Varti-Matarangas and Matarangas 2000].

A poor diversity of facies was observed for local and regional stones: in general, a single local lithology was used for most of the site, and a maximum of five different facies in total have been identified at any one site. This is illustrated in Figure 7, with the number of facies for each site shown on the left. On the right, the graphic illustrates the distribution of stones by origin, in terms of volume (%), for each site. Each site was considered globally. Allochthonous facies can be varied, but they represent less than 5% of the stone volume employed and were not used for the large ashlar blocks. With the exception of Delphi, regional and allochthonous facies represent less than 15% of the total stone volume [de Vals et al. 2020].

For all of the studied periods, a high diversity of stones (more than ten) was observed in renowned sanctuaries in particular: in Epidaurus, Delphi and the Heraeum of Argos, for example. However, the last two sites exhibit a high diversity of white allochthonous marbles: four different types were identified [Maniatis et al. 1988; Pfaff 2003]. Such detailed investigations were not undertaken for all of the archaeological sites: white marbles were generally counted as a single facies, which biases the comparison. Moreover, ten different porous allochthonous limestones have been observed in Delphi: as of now, this is considered an exception. Delphi, Epidaurus and the Argive Heraeum also exhibit medium diversity for hard limestones (more than three facies), which are absent at the four sites studied here.

These data should be qualified based on site history and geology. The archaeological sites discussed above are located within different geological settings: on the syn-rift infill of the Gulf of Corinth (present study), or directly on or next to the Mesozoic limestone basement (Delphi, Epidaurus, Argive Heraeum, Malia). Furthermore, Epidaurus, Delphi and the Argive Heraeum are located more than 10 km inland, and less expensive sea transport was prized. Epidaurus and Delphi were renowned within the Panhellenic world in Classical times, whereas Malia was a Minoan palace. This means that the builders did not have access to the same stones or the same economic resources. They also did not have the same aim: in the Panhellenic sanctuaries, the Ancient Greeks wanted to show their gratitude by building wealthy treasuries and monuments. In contrast, constructions in city-states are more practical (fortification walls, stoa, agora). These data put our study into perspective, but the comparison should be treated with caution.

4.2. Specific stones for specific uses

One regional facies recurs in all of the sites: the oolitic grainstone, a dune facies of Corinthian provenance. We do not know the exact origin: three main outcrops have been identified, in Corinth (tidal transverse dunes), near Examilia (tidal longitudinal dunes) and near Kenchreai (transverse dunes) [Collier and Thompson 1991] (Figure 2). The determination of distinctive criteria between these different dunes would require more in-depth work and sampling of the sites. At Isthmia, we hypothesise that the facies used for the Archaic Temple of Poseidon is a dune facies. We base this assumption on a recurrent pattern observed in the region: the temples of Sikyon, Perachora and Kleonai (personal observations) used the same facies of Corinthian origin.

The imported stones, regional or allochthonous limestones, were usually employed only in the temples. The Corinthian dune facies was also used for many treasures (small temples or buildings to display offerings) and for the Temple of Apollo from the 4th century BC at Delphi [de Vals et al. 2020]. Our observations confirm the conclusions of previous works [Martin 1965; Wycherley 1976], which noted that allochthonous stones were employed for large-scale public infrastructure. However, previous studies referred mostly to marbles and did not separate clearly the different “pôros”. Our conclusion is that the use of allochthonous stones concerns more specifically temples, and is applicable also to less prestigious stones (not only marbles); this includes high-porosity limestones with fine granulometry such as the oolitic dune facies in the eastern part of the Gulf of Corinth.

Local facies dominate ashlar masonry, but different materials were observed, sometimes specifically between foundations and superstructures; this includes the temples at Sikyon and Perachora (Figure 1), but also other monuments and bases, for example, the bouleuterion of Sikyon. This is common in Greek construction, even if not recurrent in our study. This pattern has been observed at other sites: the Temple of Apollo from the 4th century BC at Delphi and the second Classical temple of the Argive Heraeum both have soft limestone foundations with a hard limestone pavement [de Vals et al. 2020; Pfaff 2003].

Finally, imported stones are typically used for temples, but this was not observed in Corinth, which employed a local limestone for its Temple of Apollo. This raises the question of the dominant criterion determining the choice of building materials, if there is just one: is it a purely economic decision, or do prestige and mechanical characteristics come into play? A similar situation has been observed in Athens: the Parthenon is made entirely of marble, mostly because it was the nearest viable resource. However, we cannot answer this question for now: the Archaic Temple of Corinth, which does not include marble, is also one of the oldest temples built during the 6th century BC in the Doric style, just at the beginning of the extensive marble trade [Martin 1965].

4.3. Exploitation of the environment

Earthworks are visible inside each site and have furnished building materials, produced by small limestone quarries. In Corinth, it is plausible that the oolitic dune facies inside the city was sufficient to provide the city, at least in Greek times, but this hypothesis has yet to be verified because other large quarries near Corinth exploited similar dune facies. The small quarries near Sikyon, Isthmia and Perachora provided materials only for their respective cities: owing to their size and stone character, these quarries were not suitable for exportation. This is coherent with what is known of Greek stone exploitation: quarries were often small, episodic and tied to specific construction projects [Fant 2009].

Many small porous limestone quarries have been documented in Greece [Koukouvou 2012]. However, the lack of in-depth and consistent studies of these quarry types has prevented the determination of large-scale trends; accordingly, the prevailing knowledge of limestone exchange is certainly biased, unlike our knowledge of the marble trade [Al-Bashaireh 2021]. For example, large sedimentary stone quarries that exported their materials are known in the Greek world: the quarries of Aegina Island [Koukouvou 2012] and the quarries of the Corinth area (Examilia, Kenchreai) [Hayward 2003]. Oolitic limestone quarries are documented in Thessaly, at Tyrnavos, which furnished with building materials Larissa (17 km away), Volos (70 km away) and ancient Demetrias (next to Volos) [Melfos et al. 2016]. The Kleonai quarries [Marchand 2002], the quarries of the Asomata region in Central Macedonia [Koukouvou 2010] and the Piraeus quarries [Theoulakis and Bardanis 2000] are very large high-porosity-limestone quarries but seem to have provided building material for one unique site each (Nemea, Aigai and Athens, respectively).

Freshwater resources abound in the studied region, with monumental fountains and developed hydraulic systems at all sites, as predicted by Crouch [2004]. The builders of the sites also took advantage of the main topographic features: in Corinth, Isthmia and Sikyon, the theatres rest on the steepest slope close to the site. Faults or natural terraces caused these anomalies and revealed the unconsolidated marls underlying the hardpans. Then, the Greek builders used the marls depending on their cohesiveness: ashlar blocks were added for the seat when too soft (Corinth, Isthmia); otherwise, the seating was carved out directly (top of the theatre at Sikyon).