Pottery production and trades in south-eastern India: new insights from Alagankulam and Keeladi excavation sites

doi:10.21203/rs.3.rs-20678/v1

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Pottery production and trades in south-eastern India: new insights from Alagankulam and Keeladi excavation sites

https://doi.org/10.21203/rs.3.rs-20678/v1

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published 13 Jun, 2020

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This research is part of a wider scientific Italian-Indo project aiming to shed lights on pottery fabrication and trade circulation in the South India (Tamil Nadu region) during Early Historical Period. The recent archaeological excavations carried out in Alagankulam, a famous harbour trading with the eastern and western world, and Keeladi, the most ancient civilization centre attested in Tamil Nadu region, provided numerous fragments of archaeological ceramics, including fine ware and coarse ware potteries. Up to the typological studies, different classes of potteries were recognised, suggesting the presence of local productions and possible imports and imitations. Studied materials include common Indian products, i.e. black-and-red table wares and water jugs, along with red slipped wares, rouletted ware, northern black polished ware, which provenance identification is still debated in the current literature. In fact, for long time, the misattribution of several ceramic classes has led to wrong interpretations of the complex commercial connections between India and the Western and Eastern Mediterranean area. In this perspective, the minero-petrographic and spectroscopic investigation of several ceramic fragments from the two investigated archaeological sites would fill these gaps and provide a systematic characterization of specific ceramic classes both locally manufactured and imported. The obtained results contribute to draw interesting short-range and long-range connections in Tamil Nadu area.

Art History

Cultural Studies

Tamil Nadu

Alagankulam

Keeladi

BPNW

rouletted ware

black and red ware

Potteries represent one of the most useful archaeological artifacts in reconstructing human activity in the past. Being a part of daily use, potteries can support the interpretation of dynamics related to trade, manufacture routines, cultural and artistic traditions. The analysis of ceramic’s fabrics, including clay pastes, textures and compositional features can be used to locate the manufacture centers, as well as indicate manufacture technology and dating (in term of specific productions constrained in limited periods of time and geographic locations) (Barone, 2017; Quinn 2013). These approaches might support a better understanding and interpreting of the progress of technology and the modes of consumption in the framework of an archaeological site, as well as reconstructing the possible trade routes through ancient areas.

These aspects are particularly interesting in the case of harbours, where commercial contacts and social activities promoted goods commercialization and cultural exchanges. One running example, in the light of the archaeological and historical researches in southeast India, is the case of recent archaeological excavations carried out by the State Archaeological Department of Tamil Nadu and the Archaeological Survey of India (ASI) along the Vaigai River, Madurai, in South India. Specifically, the archaeological campaigns brought to the light new structures in the harbour of Alagankulam, and in a small village interpreted as one of the first settlement of the ancient civilization in Tamil Nadu, namely Keeladi. Although rather close each other and built in the proximity of the Vaigai River, those settlements were very different for economic and socio-cultural reasons.

Alagankulam was a very active trade centre where local production credibly co-existed with long-range imported goods. In this framework, the characterization of the local productions and the possible discrimination of imports might support interpretation on the role of the Alagankulam harbor in the cultural exchanges with Mediterranean area and the northern India and contribute to the archaeological debate on the production site locations through the Indian country. In the site, several pottery fragments were found, including transport vessels, jars, table ware, black-and-red wares, rouletted wares, northern black polished wares, and some specimens classified as Fine Grey Potteries. Contrarily, long –distance or overseas trades are unreliable in the inner part of the country; here, few shapes were found, mainly consisting of daily-use pottery types, such as domestic vessels enclosing cooking pots and water jars with narrow and short neck and globular body (coarse red ware, CRW) and traditional black-and-red table wares (BRW).

Looking at the different ceramic classes found in the two sites, they can be used as chronological and contextual indicators. Detailing, the term black-and-red ware (BRW) we refer to a class of artefacts generally attributed to a long-lasting Indian tradition (since the beginning of the I millennium B.C.) and appearing both red and black in colour. According to literature, they were produced by positioning upside down the vessels in the kiln with some vegetal materials inside; the outside part, subjected to oxidizing condition tuned in red, while the inner surface and the rims, under reducing conditions, turned in black (Singh, 2009). This class of vessels is largely attested in several site through India, with an important variability in fabric and manufacture technology reflecting the different geographical context in which they had been produced. Along with BRW, black ware (BW) is a class of vessels largely attested in India from the first half of the I millennium and with a lost-lasting tradition (Schenk, 2006). Again, they are attested with various fabrics, according to the local raw materials used for the production.

Part of the luxury ware repertoire, the North Polished Black Ware (NPBW) represents a class of vessels largely exhibited though India; its production, spread just after the so called Gray Painted Ware culture, is traditionally located in the area of the Ganga Plains (Uesugi, 2018). In respect to periodization, a recent revision based on different archaeological stratigraphy dated the NPBW production between VII B.C. to I B.C. (Uesugi, 2018; Sharim, 2011). NPBW is characterized by a lustrous black slip glossy surface obtained in the Indian tradition by the application of a refined clay slip and an organic liquid after being fired under reducing conditions (Sharim, 2011; Maritan, 2019).

A class of very fine, luxurious pottery sherds attested in India is represented by the so called “Fine Grey Potteries”, recently recognized as a group of imported vessels from Northern Indian areas (Schenk, 2015); overall, for long time some of these vessels were interpreted as Roman productions (Wheeler, 1946; Begley, 1988; Gogte 1997, 2001; Coningham, 1999; Ford, 2005; Schenk 2014) (The misattribution was due to their fine quality, the slipped fabric (red or black) (Wheeler, 1947; Tomber, 2008) and their wide distribution in Sri Lanka and eastern India, in the far East (e.g., in Indonesia), in Egypt, and in Bernike harbour. Amongst the fine grey potteries, the rouletted ware is characterized by its hard glossy surface and its compact clay paste; it is easily identified by a distinct decoration pattern, due to bands of indentions with different shapes, as lines, dots, diamonds and triangles, made using a roulette (Begely 1988). Recent studies on rouletted wares (RW) found in Sri Lanka, Vietnam, India and reference clays from Chandraketugarh would suggest the Ganges Valley as probable source of clay materials for the manufacture of this peculiar fine ware class (Schenk, 2014; Gogte, 1997, 2001). Up to the current literature, the Indian provenance of rouletted wares seems largely accepted and their occurrence in archaeological sites would testify the involvement of them in the intense Indian trades within the Indian Ocean and the Mediterranean regions. As far as dating, the production of RW is usually placed between II BC and I AD, predating any appearance of Roman sigillata in India (Tomber, 2008; Schenk, 2015) and testifying a network exchange earlier than Roman period. According to the Tissamaharama pottery sequence and the recent periodization proposed by Schenk (Schenk, 2015), it looks like RW circulated for a limited time interval (in Tissamaharama the first fragment is dated II BC), specifically till the I BC, promoting the production of later local imitations discriminated from the genuine ones for their coarse-grain clay paste.

Red polished ware (RPW) constitute another interesting class of the so-called Fine Grey Potteries imported from the Northern areas of India. Again, this class of potteries were misinterpreted due to similarities with terra sigillata; however, the discovery of RPW along the Persian Gulf and the recent studies attributing it to Indian production, make it possible to consider RPW as indicator of connections within the Indian Ocean of the Periplus-time (Schenk, 2015). According to literature, this class of ceramics exhibit typical shapes consisting in ritual vessels (i.e., spouted jugs and sprinklers). Finally, sigillata ware is the most debated ceramic class among the Indian findings; its occurrence and identification are largely questioned since the Wheeler discoveries at Arikamedu (Wheeler, 1946), and the Begley’s reconsiderations (Begley, 1988). Up to our knowledge, the attribution of sigillata ware has to be carefully evaluated, considering that different sigillata productions attested in such different periods, were traded in India, namely the Italian, the Eastern Sigillata A (from Syria) and the Eastern Sigillata B (from Western Asia Minor). Thus, the attribution of sigillata ware need a careful examination of the archaeological context and the dating of pottery sequence.

This study therefore aims to enlarge knowledge on pottery fabrication and trade circulation in the Southeast India (Tamil Nadu region) by analysing two set of potteries from the famous ancient harbour of Alagankulam and the inner village of Keeladi by minero-petrographic, chemical and spectroscopic methods. The obtained results allow to provide a characterization of ceramic productions in the Tamil Nadu region, depict a preliminary frame on the relations between the two sites, interpret commercial contacts and good exchanges, get the basis for a reference database of Indian Tamil productions.

Algankulam is considered as the ancient harbor of Madurai, in the southeastern India (Figure1). According to the historical sources, Madurai was the capital of Pandya Kingdom. Pandyas was well known to Greeks and Romans, so that trade and commercial relations were established since the II century B.C., as documented by local inscriptions (Sangam literature) and Roman authors, such as Strabo (25 B.C.) and Pliny (75 B.C.). The archaeological excavation carried out by the State Archaeological Department of Tamil Nadu in 2005 brought to the light numerous ceramic records, mainly including fine ware and amphorae, with a variability in composition and shape related to difference provenance of the artifacts. Alagankulam site was the official harbor of the Pandya kingdom as well as the incoming and distribution center for goods within the south-eastern region of India; thus, it is plausible to hypothesize the concomitant presence of local productions and imitations, as well as imports. Based on radiocarbon dating of the strata (State Archaeological Department, Tamil Nadu, personal communication) the occupancy of the site is attested since IV-III century B.C., while the more recent excavated strata pertain to I century B.C. – I century A.D.

Keeladi, located 12 km southeast of Madurai and 2 km from the River Vaigai on its northern side (See figure1), is an archaeological center dated back to Sangam Era. The site was extensively excavated by the State Archaeological Department of Tamil Nadu in 2017 with the exploration of 15 trenches excavated along their stratigraphy. As far as the chronology (State Archaeological Department, Tamil Nadu, personal communication,), the first occupancy of the site is dated back to VI-V century B.C., while the more recent strata are dated to the II-I century B.C.

The analysed ceramic corpus

In this study twenty-nine pottery fragments representative of the classified typological classes have been selected and analysed, namely twelve samples from Alagankulam site (labelled as A_#, Figure 2), and seventeen from Keeladi archaeological site (labelled as K_#, Figure 3) (Table 1).

Among the identified productions in Alagankulam, the pottery corpus selected for this study is dated between the II century B.C. to the I century B.C. - I century A.D. and includes Black Rouletted ware (RW, A15), sigillata ware (A16), Grey ware (GW, A17), Black ware (BW, A18), Red roulette ware (RW, A19), Red ware (RDW, A20), Black-and-red ware (BRW, A21), Northern Black polished ware (NBPW, A22). As far as it concerns Keeladi’s excavation site, two main classes were identified: Coarse Red ware (CRW: K1, K4, K5, K6, K11, K12), and Black-and-red table-wares (BRW: K3, K7, K8, K9, K10, K14, K15, K17), interpreted as local production largely attested in Tamil Nadu region. Only two examples of Red slipped ware (RSW: K2, K16) are attested. Up to the dating of the strata, BRW are testified along the entire excavated strata (from the V to the II-I century BC), CRW are attested in the strata dated back to III-II century B.C., while red-slipped ware are attested only in the later phases (II-I century B.C.).

Experimental

Preliminary observation of the samples were carried out to characterize the ceramic’s clay paste and provide a photo-documentation of the samples by using a stereomicroscope equipped by a Color Microscope Camera ZEISS Axiocam ERc 5s. The minero-petrographic and textural features of the studied samples were recorded by thin section analysis using an Optical Microscope (OM). Potteries were classified according to Whitbread method (Whitbread, 2017) allowing to group different fabrics on the bases of clay matrix, microstructure and aplastic fraction characteristics. XRD diffraction (XRD) has been performed on a selection of 13 powdered samples, representative of the identified petrographic fabrics, by using a Bruker D2 PHASER to investigate the bulk mineralogical composition. Nondestructive spectroscopic investigations were carried out directly on fresh cut surface by using the Bruker ELIO portable ED-XRF spectrometer equipped with an SDD detector and an X-Ray tube with Rhodium anode. The measuring spot on the surface is about 1 mm in diameter. The XRF spectra were acquired on fresh cut surface; the operational parameters were: 60 s acquisition time, 20KeV tension and a current of 80 μA. For each sample, two different points on the bulk have been measured to ensure the repeatability of the experiment. Although a full quantitative analysis of the samples is impossible, given the inability of portable ED-XRF instruments to detect light elements, it is still possible to exploit the Fundamental Parameter Method (Solè, 2007) for obtaining a rough estimate of the elemental concentrations an their variation from one sample to the other. Two different points on the samples were measured, and the elemental concentrations obtained with the Fundamental Parameter Meter were averaged. The elemental concentrations estimated using this method can be used as input for a Principal Component Analysis and the consequent determination of possible clusters.

Moreover, on the decorated surfaces, Raman analysis were carried out by using a Renishaw In Via Spectrograph with a multichannel air-cooled CCD detector, equipped with a He-Ne laser (633 nm) operated at the nominal power of 0.6 mW with an Olympus 50X objective. The spectral resolution of the instrument is about 0.5 cm^-1 and the spectral range analyzed between 100 and 3200 cm^-1. Typical measurements conditions were 10 s integration time and 10 accumulations. The laser power was set to avoid possible degradation of the sample. The spectral calibration of the instrument was performed on the 520.5 cm⁻¹ band of a pure silicon crystal.

Minero-petrographic characterization

The thin section observation carried out on potteries from Alagankulam allowed to classify two petrographic fabrics: fabric AGM-1, exhibiting silty and fine-grained matrix without tempers, and fabric AGM-2, including only one sample (A21), with a silty ceramic paste and coarse-grained aplastic fraction.

In detail, Fabric AGM-1 (A15, A16, A17, A18, A19, A20, A22, (Figure 4.a-c) includes all the fine-grained table wares found in Alagankulam; samples are characterised by silty, micaceous matrix, ranging from orange in A19 (RW) and A20 (RDW), to brown-grey in A15 (RW), A16 (SW), A17 (GW), A18 (BW), and A22 (NBPW). Optical activity ranges from medium to high, usually higher in the core, except for sample A16 where is absent or very low. Microstructure is due to irregular and elongated voids, with a slight low porosity. Some of the voids are due to fossil tests and fossil mould. The aplastic fraction is always very fine (< 50 µm), showing high depuration of the raw materials, including quartz and white mica. Round iron-rich ACF (Acf: amorphous concentration features) are presents, together with secondary recrystallization calcite on the rims or in the bigger pores.

The only black-and-red ware (BRW), namely A21, constitutes the Fabric AGM-2 (Figure 4.d). The ceramic paste is characterized by silty matrix, dark brown in colour. Optical activity is from medium to low. Microstructure is mainly due to elongated micro-pores (opening max<50μm), with a clear preferential orientation, interesting the whole structure and attributable to the addition of fibres. Rare fossils (foraminifera) are present as fossil moulds or fossil tests. The aplastic fraction, rather abundant (~40 - 50%,), is from sub-rounded to sub-angular in shape, with polymodal grainsize distribution. Aplastic fraction is due to fractured quartz, feldspars, among which plagioclase, altered feldspars with evidences of perthite mixing, preferentially oriented micas, amphibole, pyroxenes, biotite lamellae, rare zircon, titanite, ilmenite, magnetite. Mafic granulite rock fragments are also present within the coarser fraction, indicating a probable smashing and intentional addition of tempers.

The use of highly depurated clays for the manufacturing Fabric AMG-1 samples is also confirmed by the mineralogical composition detected by XRD diffraction analysis (Table 2), where the use of illite-based clays with quartz and feldspar are identified. The inspection of XRD patterns didn’t show any additionally diagnostic mineralogical phase neither any relevant discrimination criteria among the analysed sherds. On the contrary, the mineralogical analysis performed on sample A21 do not show any traces of illite-muscovite, but the presence, in low amount, of a different mineralogic suite, containing anorthite, amphibole, pyroxene, ilmenite and titanite, suggesting a different manufacture procedure and different raw materials respect to the other ceramic classes.

As far as it concerns the samples from Keeladi, petrographic analysis allowed discriminating two main different fabrics, along with two singularities. In detail, Fabric KLD-1 includes shapes identified as water jars (samples K1, K4, K5, K6, K11, and K12) characterised by an orange body-paste, with silty micaceous matrix, abundant biotite lamellae and mafic granulite rock fragments. Fabric KLD-2 (K3, K7, K8, K9, K10, K14, K15, K17) include black-and-red (BRW) pots; this fabric is discriminated from KLD-1 for its finer grainsize distribution and it is characterised by a black body-paste, with silty micaceous matrix, abundant biotite lamellae and mafic granulite rock fragments. Finally, the two singularities include red polished wares (RPW): Fabric KLD-3 includes sample K2, characterised by granitic rock fragment, and Fabric KLD-4 (K16) characterised by a dark core and a micaceous matrix.

In Fabric KLD-1 (CRW, K1, K4, K5 K6, K11, K12; Figure 5.a-b) the matrix is silty, ranging from ochre-brown to ochre in colour with grey core, attributable to temperature gradient during firing. Optical activity is from high to medium, with a variability resembling the colour and credibly the firing conditions. The textural features would suggest a poor selection of raw materials. Microstructure is mainly due to elongated pores, from opening_max < 50μm to opening_max < 400 μm. Irregular voids are also present, reaching 700 μm in dimension. Rare fossils (foraminifera) are present as fossil moulds or fossil tests. The aplastic fraction, rather abundant (about 40%), from sub-rounded to sub-angular in shape, with polymodal grainsize distribution ranging from 50 μm to over 1 mm in dimension. Aplastic fraction is due to fractured quartz, feldspars (some of which exhibiting perthite mixing), plagioclase, altered feldspars, biotite lamellae, micas (exhibiting preferential orientation), amphibole, pyroxenes, titanite, ilmenite, magnetite, and rare zircon. Mafic granulite rock fragments are also present within the coarser fraction, indicating a probable smashing and intentional addition of the temper fraction. Secondary recrystallization phases are also present, along with other secondary phases related to burial environment. Red and black iron-rich ACF (depletion) and clay cloths are finally detected.

In samples grouped in Fabric KLD-2 (BRW, K3, K7, K8, K9 -Fig.3.d, K10, K13, K14, K15, K17; Figure 5.c-d) the matrix is silty, dark brown in colour with a surface slip ranging in thickness from 50 to 500 µm. Optical activity is from high to medium-low, depending on the different firing conditions. Microstructure is mainly due to elongated micropores (opening max<50μm), with a clear preferential orientation, interesting the whole structure and attributable to the addition of fibres/organic matter. Bigger elongated pores (opening max<400μm) and irregular voids, reaching 700 μm in dimension are present, especially in samples K7, K13, and K17, exhibiting a different texture. The aplastic fraction, rather abundant (from 40% to 50%, reaching 70% in K17), is from sub-rounded to sub-angular in shape, with polymodal grainsize distribution (from 50 μm to 500 μm in dimension). Aplastic fraction is due to fractured quartz, feldspars, among which plagioclase, altered feldspars with evidences of perthite mixing, preferentially oriented micas, amphibole, pyroxenes, biotite lamellae, rare zircon, titanite, ilmenite, magnetite. Mafic granulite rock fragments are also present within the coarser fraction, indicating a probable smashing and intentional addition of tempers.

As far the singularities, sample K2 (RPW) constitutes Fabric KLD-3 (Fig.5.e); it is characterised by silty matrix, homogenous, reddish-yellow in colour, with high optical activity. Microstructure is mainly due to elongated voids, exhibiting a preferential orientation. The aplastic fraction exhibits a polymodal grainsize distribution with granitoid rock fragments, quartz and feldspar, rare zircon and pyroxene. Abundant red ACF (depletion) are present. Finally, sample K16 is classified as Fabric KLD-4 (RPW, Fig.5.f); the matrix is clayey, micaceous, orange in colour, with a black core in the centre. Microstructure is mainly due to elongated, iso-oriented micropores. Aplastic fraction (about 40%) exhibit a polymodal grain-size distribution, due to quartz, feldspar, micas, and pyroxenes. The aplastic fraction (40%), from sub-rounded to sub-angular in shape, exhibit a polymodal grainsize distribution, reaching 600 μm in dimension. It is due to fractured quartz, feldspars (some of which exhibiting perthite mixing), plagioclase, altered feldspars, biotite lamellae, micas (exhibiting preferential orientation), amphibole, pyroxenes, titanite, ilmenite, magnetite, and rare zircon. Dry clay pellets are also present. The mineralogical composition of a selection of samples representative of the identified petrographic fabrics was determined by X-ray diffraction (XRD). Overall, the identified mineralogical phases match well with the thin section observations, confirming the identified compositional groups (Table 3). In detail, coarse red ware (CRW) potteries are characterized by illitic-clays and absence of newly formed minerals, according to the variability of the optical activity from high to medium-low; credibly, calcite-poor clays fired in not-homogenous furnace conditions were used. Black-and-red ware (BRW) potteries exhibits a similar mineralogical composition respect to CRW, due to the occurrence of similar aplastic fraction; however, different clays (not-illitic in composition) were used to manufacture this specific shapes; the absence of newly formed minerals and the high-medium optical activity would suggest the use of calcite-poor clays fired at high temperatures. Finally, red polished ware do not exhibit mineralogical composition quite in accordance with thin section observation.

Chemical composition and surface features

Multivariate statistical analysis was applied on chemical data (Table S1) to highlight chemical-based discrimination criteria among the analyzed potteries. In Figure 6 the plot corresponding to the first two Principal Component, and the corresponding loading plot are reported. The total variance expressed by the first two components is 73.5%. The inspection of the diagrams allows to discriminate two main groups, according to petrographic observation. A fist one includes all samples from Keeladi (coarse red ware, CRW, and black-and-red ware, BRW) along with the only one black-and-red ware artifacts from Alagankulam (sample A21). Moreover, the red slipped ware represented by the sample K2 is separated from this field, suggesting a not-local manufacture. A second field is represented by all fine ware artifacts from Alagankulam; it is interesting to note that no relevant compositional differences can be observed among the archaeological typologies, suggesting a common provenance.

Raman Analyses

With a peculiar focus on black-and-red ware (BRW), the Raman spectra collected on slipped surface evidenced the presence of carbon black and hematite, respectively (Figure 7). The analyzed black decorations, in fact, reveal the main peaks of amorphous carbon with characteristic absorption peak at 1610 cm^-1and a broad peak at around 1390 cm^-1 (Lluveras-Tenorio, 2019); the Raman spectra of the red decoration, instead, present the typical peak at 290 cm^-1 together with the medium intensity band at 223, 407, 609 and 1334 cm^-1 characteristics of the Haematite (De Faria, 1997) (Fe₂O₃), a broad band at 661 cm^-1 can be assigned to Magnetite trace (Fe₃O₄), probably due to a not complete transformation; same white crystal are also present and many of them are identified as Calcite (CaCO₃) and Quartz (SiO₂).

Discussion

Despite the variability in shape and typologies, the majority of the potteries found in Alagankulam present similar minero-petrographic features, i.e. fine depurated clay pastes and fine glossy surface, some of which decorated with typical rouletted patterns. Unfortunately, minero-petrographic features do not provide diagnostic mineralogical assemblages; on the contrary, chemical analysis reveal a quite compositional homogeneity among the different archaeological typologies, suggesting a common provenance. Up to literature, it is quite accepted that the overall fine luxury ware repertoire represents imports from the North, and in particular from Ganges Valley. Quite interesting is the case of the sample classified as sigillata (A16), grouped in the same compositional field of the other fine ware artifacts. Actually, the only coeval comparisons can be found in Eastern Sigillata A, which production centers are located in Eastern Mediterranean area during Roman age (II century B.C. - II century A.D.). However, the chemical similarities with the North Indian imports would suggest a misclassification of the pottery, possible representing an example of red slipped ware.

Another interesting evidence is the occurrence of only one sample of Black-and-red ware (BRW, A21) selected among the Alagankulam corpus, exhibiting the same petrographic and chemical features of Keeladi materials. This class of artifacts in Keeladi is in fact characterized by a typical mineralogical assemblage highly compatible with local geological outcrops characterized by pyroxene granulites and charnockite gneiss (Sajeev, 2005 ; Geological Survey of India 1995) thus, as expected, for this traditional long-lasting production a local manufacture can be assessed. The evidence of black-and-red imports from Keeladi to Alaganlulam has interesting cultural implications; it is possible to assume that BRW were imported from the surrounding areas, like Keeladi, where workshops were specialized in common ware fabrications. The Raman analysis carried out on the black and red surfaces of BRW class confirm the hypothesized inverse firing routine; the detected carbon on the rims can be thus considered a residue of the organics used during firing in the kiln to produce reducing atmosphere. Regarding the other representative class of artifacts recovered in Keeladi, i.e. the coarse red ware (CRW), the mineralogical assemblage of the aplastic fraction is highly compatible with the local geology, with similarities with the BRW production. However, these two class of vessels exhibit a different mineralogical composition of the clay (illitic vs not-illitic clay), different microstructural features (in term of porosity and pore size distribution) and different sorting of the tempers (coarser in BRW, finer in CRW) so that it is possible to propose the use of different sources of local clays, characterized by aplastic fraction related to the same parental rocks (i.e., pyroxene granulites and charnockite gneiss), differently selected to produce as much as different typologies of vessels. It is worth of note that in Keeladi the technological routine employed to obtain RBW and CRW is unvaried over the time; particularly, compositional and textural features are over all the studied stratigraphy, testifying the convey of technology and raw material source exploitation over all the site occupancy. Finally, in respect to RPW, up to literature this class of artifacts is usually attributed to Northern Indian sites from Ganges Valley to Gujarat; (Schenk, 2014; Tomber, 2008); however, we know that in some archaeological context the import of peculiar classes promoted the production of local imitations. This could be the case of the two studied fragments of RPW; in particular, sample K16 would match with the local geology, suggesting a local imitation practice; otherwise, sample K2 is characterized by granitoid rock fragments, not compatible with the local outcrops. Chemical data seems to confirm this hypothesis; the sample is in fact out of the two observed compositional fields. Looking at the regional geological framework, a possible source area for this production could be located in the neighbors of Tiruchirappalli region, where granites outcrops occur (Geological Survey of India 1995). This evidence would suggest the presence of both local productions and imports of Red slipped ware, circulating at regional scale.

To our knowledge, this research constitutes one of the very few archaeometric studies on a coherent corpus of ancient ceramics from South-India archaeological contexts. Specifically, the study contributes to provide information regarding the occurrence of the imported group of ‘Fine Grey Pottery of Northern Indian Origin’ in Alagankulam, proving its role in the complex connective tissue of the India Ocean even prior than the Roman trades. Moreover, the study provides a homogenous reference group for local BRW and CRW produced in south-east India, and interesting clues on RSW, testifying the practice of local imitation imported at regional scale. This study is only part of a wider project aimed to unveil the complex trade routes in the ancient world and support the archaeological interpretation about the debated “Roman-Indo” connection between Mediterranean regions and South-East India. To purse this objective, advanced investigations are currently ongoing on another class of ceramics, namely transport vessels, particularly suitable in supporting the drawing of ancient trade routes within and beyond the Indian Ocean.

Acknowledgments

The authors acknowledge the Archaeological State Department, Tamil Nadu, and the archaeologists working at Alagankulam and Keeladi sites for having provided the studies samples. T.S. and J. P. acknowledge the Visiting Fellow program of the University of Pisa for having supported their research mobility to Italy.

Availability of data and materials

All data generated or analysed during this study are included in this published article and its supplementary information file.

Competing interests

The authors declare that they have no competing interests

Funding

Not applicable

Authors’ contributions

E.O.: Investigation, Data acquisition, Writing - original draft, Writing - review & editing. T.S.: Conceptualization, Investigation, Data curation, Methodology, Writing - review & editing. J. P.: Investigation, Data acquisition. V.P.: Investigation, Data acquisition, Writing - original draft, Writing - review & editing. S. L.: Investigation, Data acquisition, Writing - original draft, Writing - review & editing. S.R: Project administration, Conceptualization, Investigation, Data curation, Methodology, Writing - original draft, Writing - review & editing.

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Table 1. List of analysed samples, along with information on color, typology and dating.

Sample N°	site	Munsell Colour (exterior)	Munsell Colour (paste)	Class
A15	Alagankulam	7.5YR 5/1	7.5YR 5/1	Rouletted ware (black) (RW)
A16		7.5YR 4/3 + 7.5YR 6/6	7.5YR 5/1	Sigillata
A17		7.5YR 6/1	7.5YR 6/1	Grey ware (GW)
A18		5YR 2.5/1	7.5YR 3/1	Black ware (BW)
A19		5YR 6/8	5YR 6/8	Rouletted ware (red) (RW)
A20		7.5YR 6/8	7.5YR 6/8	Red slipped ware (RSW)
A21		5YR 2.5/1+5YR 5/8	7.5YR 5/2 +7.5YR 5/7	Black-and-red ware (BRW)
A22		5YR 2.5/1	7.5YR 3/1	Northern Black Polished Ware (NBPW)
K1	Keeladi	7.5YR 5/6	7.5YR 5/6 + 7.5YR 5/2	Coarse Red Ware (CRW)
K2		5YR 4/6	7.5YR 6/8	Red Slipped ware (RSW)
K3		5YR 2.5/1+ 7.5YR 5/8	7.5YR 5/2	Black-and-red ware (BRW)
K4		5YR 3/3	5YR 4/6	Coarse Red Ware (CRW)
K5		7.5YR 6/4	5YR 5/6	Coarse Red Ware (CRW)
K6		5YR 5/8	5YR 4/6	Coarse Red Ware (CRW)
K7		5YR 2.5/1+ 5YR 4/6	7.5YR 2.5/1+5YR 5/2	Black-and-red wares (BRW)
K8		5YR 2.5/1+ 7.5YR 5/8	7.5YR 5/1+ 5YR 6/4	Black-and-red wares (BRW)
K9		5YR 2.5/1+ 5YR 5/6	5YR 4/1 + 5YR 5/4	Black-and-red ware (BRW)
K10		5YR 2.5/1	7.5YR 3/1	Black-and-red ware (BRW)
K11		5YR 5/8	5YR 5/3 + 5YR 5/8	Coarse Red Ware (CRW)
K12		5YR 4/6	5YR 4/6	Coarse Red Ware (CRW)
K13		5YR 5/8	7.5YR 2.5/1	Black-and-red ware (BRW)
K14		5YR 2.5/1	5YR 3/1	Black-and-red ware (BRW)
K15		5YR 2.5/1+ 5YR 5/4	7.5YR 2.5/1	Black-and-red ware (BRW)
K16		5YR 5/8	5YR 5/8 + 5YR 2.5/1	Red Slipped ware (RSW)
K17		5YR 2.5/1+5YR 5/6	7.5YR 2.5/1	Black-and-red ware (BRW)

Table 2. Semi-quantitative data on mineral phases detected by XRD analysis for samples from Alagankulam. (x) is related to the relative phase abundance; tr = traces.

Sample ID	Petrographic Fabric	Class	Quartz	Albite	Anorthite	Orthoclase	Amphibole	Pyroxene	Illite/muscovite	Ilmenite	Titanite
A 15	AGM-1	RW (black)	xxx	xx					xx
A 16	AGM-1	Sigillata	xxx	xx					xx
A 17	AGM-1	GW	xxx	xx					xx
A 18	AGM-1	BW	xxx	xx					xx
A 19	AGM-1	RW (red)	xxx	xx					xx
A 20	AGM-1	RPW	xxx	xx					xx
A 22	AGM-1	NBPW	xxx	xx					xx
A 21	AGM-2	BRW	xxx	x	x		tr	tr		tr	tr

Table 3. Semi-quantitative data on mineral phases detected by XRD analysis for samples from Keeladi. (x) is related to the relative phase abundance; tr = traces

Sample ID

Petrographic Fabric

Class

Quartz

Albite

Anorthite

Orthoclase

Amphibole

Pyroxene

Illite/muscovite

Ilmenite

Titanite

K 1

KLD-1

CRW

xxx

K 4

KLD-1

CRW

xxx

K 5

KLD-1

CRW

xxx

K 6

KLD-1

CRW

xxx

K 12

KLD-1

CRW

xxx

K 3

KLD-2

BRW

xxx

K 9

KLD-2

BRW

xxx

K 13

KLD-2

BRW

xxx

K 14

KLD-2

BRW

xxx

K 2

KLD-3

RPW

xxx

K 16

KLD-4

RPW

xxx

Table S1. Chemical composition of the analyzed samples. Elemental concentration was estimated by Fundamental Parameters method.

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Pottery production and trades in south-eastern India: new insights from Alagankulam and Keeladi excavation sites

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