Dietary perspectives on social asymmetry in a full Iron Age community of northern Italy: stable isotope evidence from the Patavine CUS-Piovego necropolis

Food consumption represents a key dimension of social inequality in past societies, as it reflects not only subsistence strategies but also cultural practices, economic organisation, and differential access to resources^1,2,3. Stable isotope analysis of human remains has become a key method for reconstructing past dietary practices and assessing their broader social implications. Numerous studies across Europe have demonstrated that dietary variability was structured by social hierarchy, revealing patterns of inequality during the Bronze and Iron Age^{4,5,6,7,8,9,10,11}.

Despite the increasing application of isotope approaches in European Iron Age contexts, northern Italy remains notably underrepresented in this field. To date, only two stable isotope studies on Iron Age human remains from this region have been published: the Buco del Diavolo site in western Liguria, dated to the Final Bronze Age/Early Iron Age transition (10th -9th centuries BCE)^12,13, and the Seminario Vescovile necropolis in Verona, dated to the 3rd -1st centuries BCE, including a period of advanced Romanisation¹⁴. As a result, there is currently a lack of dietary isotope data for the Early and Middle Iron Age (9th -4th centuries BCE), a period marked by profound cultural, economic, and socio-political transformations in northern Italy, with trajectories that varied significantly across regions¹⁵.

The scarcity of isotope data is largely explained by the overwhelming predominance of cremation rites in Iron Age northern Italy, which preclude the recovery of collagen necessary for stable isotope analysis¹⁶. This limitation is, however, largely period-specific and consistent with broader European patterns, where chronological gaps in isotope datasets are often observed for this period^17,18.

Nevertheless, during the Early Iron Age in Central Europe, cremation ceased to be the sole funerary rite, giving way to a broader range of practices, including inhumations in burial mounds, bi-ritual graveyards, and new forms of cremation graves¹⁹. Therefore, although representing a minority practice, inhumations offer an invaluable opportunity to investigate the interplay between diet, identity, and social organisation in this period. Consistently, in Veneto, inhumation coexisted with cremation from the Late Bronze/Early Iron Age onwards, and its selective use has been hypothesised to reflect social distinctions, with inhumed individuals possibly representing socially marginal or otherwise distinct groups^20,21,22.

This study presents new carbon (δ¹³C) and nitrogen (δ¹⁵N) isotope data from inhumed individuals from the bi-ritual necropolis of CUS-Piovego in Padua, dated between the mid-6th and 4th centuries BCE. As one of the most extensively investigated funerary contexts that was active during Padua’s transition to full urbanisation^22,23, this site represents one of the most significant funerary contexts currently available for exploring the social and cultural dynamics of pre-Roman Padua during its urban development and can serve as a valuable model for understanding broader patterns across the Veneto region.

This contribution aims to investigate dietary practices among the inhumed individuals of the CUS-Piovego necropolis and to assess whether their isotope values are consistent with long-standing archaeological interpretations linking inhumation to socially marginal or distinct groups in Iron Age Veneto^{20,21,22,24,25,26}. Although the absence of comparative isotope data from cremated individuals prevents a direct assessment of potential dietary inequality, the results from the inhumed subset allow for a nuanced discussion of the social and cultural foundations of bi-ritualism (i.e., the coexistence of cremation and inhumation practices within the same funerary space) in the region.

In recognition of the inherent biases in interpreting funerary evidence – stemming not only from the archaeological record but also from the cultural frameworks of past societies^27,28,29– this study adopts a multi-proxy approach, integrating bioarchaeological, isotope, and archaeological data to support more nuanced interpretations of the relationship between diet, social hierarchy, and cultural practices in Iron Age northern Italy.

The archaeological background

The CUS-Piovego necropolis is located in the eastern part of modern city of Padua, between the Piovego and Roncajette canals, in an area where the ancient course of the Medoacus River once flowed out of the city²³(Fig. 1).

Following the Iron Age funerary codes in the Veneto region, both cremation and inhumation rites are attested at the site²³. The excavations carried out by the University of Padua recovered 140 cremations, 26 inhumations, 6 horse burials, and a rare case of human-horse co-burial^22,23,30. However, unlike the other necropolises in Padua, which were established in the late 9th – early 8th centuries BCE and remained in use until the Roman period^31,32,33, the CUS-Piovego necropolis was founded in the first half of the 6th century BCE, a period corresponding with Padua’s consolidation as an urban centre²³. For this reason, within the broader funerary landscape of the Veneto region, the CUS-Piovego necropolis is a key site for investigating the socio-political transformation dynamics occurring in Padua during the Middle Iron Age.

In particular, the foundation of the necropolis has been interpreted as reflecting the integration of a foreign group into the local community²³. Supporting this interpretation is the onomastics of Tival- Bellen-, whose Celtic-rooted name appears on a porphyry ciottolone (i.e., a large stone pebble, a kind of monument typical of the Iron Age Veneto tradition) discovered within the necropolis²³. Tival- Bellen- is regarded as the progenitor of the Andeti family group^23,34, a lineage that rose to prominence within local Patavine society and successfully preserved its elevated status even following the Roman colonisation of the region^35,36,37.

At the CUS-Piovego necropolis, most burials date between the mid-6th and the 4th centuries BCE, with the site’s use ceasing in the 4th century BCE²³. As observed in other contemporary necropolises, at the site, cremation burials are often accompanied by grave furnishings that may be elaborate and occasionally highly prominent, whereas inhumations tend to lack such offerings. When present, the inhumation grave goods are minimal, typically limited to a metal fibula likely used to fasten the burial shroud²². At the CUS-Piovego necropolis, some inhumed individuals exhibit atypical burial treatments. Notably, four burials were found in a prone position²², a body arrangement that has sometimes been interpreted as indicative of social deviance or marginality in archaeological literature³⁸. However, evidence from Iron Age Europe indicates considerable variability in body positioning, including flexed, contracted, and seated inhumations, suggesting that non-supine positions may occur within normative funerary contexts rather than representing exceptional or marginal practices^19,39,40,41.

Among the prone burials from the necropolis, Tomb IX contained a young woman buried in a prone position with her arms and legs tied behind her back²². Another exceptional case is Tomb UFC 12, which contained a young male individual lying supine above a horse, both deposited in the same pit^26,30. This burial was associated with a large in doppio dolio cremation (Tomb UFC 2), a tomb typology generally indicative of high-status contexts. Furthermore, the horse exhibits evidence of blunt force trauma to the skull³⁰. On this basis, the assemblage has been interpreted as the co-burial of a stable attendant and a horse, possibly ritually killed in honour of a high-ranking individual who was cremated nearby²⁶. However, the associated cremation tomb had been largely disturbed in the past and, although its architectural features suggest that it may once have belonged to an individual of elevated status, the surviving evidence is too fragmentary to support this interpretation conclusively. Moreover, no data on the grave goods or human remains from this cremation were available for analysis.

Taken together, the archaeological and funerary evidence from CUS-Piovego provides a crucial contextual framework for exploring the relationship between burial practices, social differentiation, and diet in Iron Age Veneto.

δ¹³C and δ¹⁵N in human and faunal bone collagen

Supplementary Tables S1 and S2 present the list of skeletal elements analysed for collagen δ¹³C (δ¹³C_VPDB) and δ¹⁵N (δ¹⁵N_AIR) isotope values. Figure 2 shows the δ¹³C and δ¹⁵N results for the human and faunal samples. The isotope values and quality control indicators are reported in Supplementary Tables S3 and S4. Specifically, 15 out of 39 samples (7 human and 8 faunal) failed to produce sufficient collagen for analysis and were therefore excluded. For the remaining samples (12 human and 12 faunal), C:N ratios ranged from 2.9 to 3.6, which is indicative of acceptable collagen preservation⁴². However, some samples yielded relatively low collagen amounts, falling below the 1% threshold suggested by Van Klinken⁴³, indicating variability in collagen preservation across the sample.

In the human sample, isotope data are available for only 2 males and 9 females, limiting robust comparison between sexes. The human sample shows mean δ¹³C and δ¹⁵N values of − 13.7 ± 1.5‰ and 11.2 ± 0.9‰, respectively (Supplementary Table S3). δ¹³C values in males are − 13.6‰ (Tomb V, aged > 40 years old at death) and − 11.6‰ (Tomb XIV, aged 30–35 years at death), with corresponding δ¹⁵N values of 11.4‰ and 11.6‰, respectively. In females (n = 9), δ¹³C values range from − 17.6‰ to -12.2‰, while δ¹⁵N values range from 9.7‰ to 13.1‰.

Using Tukey’s interquartile range method [or Tukey’s fences [Q1 – k(Q3-Q1), Q3 + k(Q3-Q1)], with k = 1.5;⁴⁴] applied to the full set of human values, δ¹³C values span from − 16.5‰ to − 10.3‰, with a single outlier identified (Tomb IX: δ¹³C = − 17.6‰). δ¹⁵N values range from 9.4‰ to 12.9‰, with one outlier (Tomb XI: δ¹⁵N = 13.1‰), an infant aged around 1.5 years at death (Supplementary Figure S2). The elevated δ¹⁵N value in this individual is consistent with the effects of breastfeeding^45,46. Enamel peptide analysis identified this infant as a female (Supplementary Figure S1).

Notably, four females in the sample (Tombs I, IV, IX, and XX) exhibit lower δ¹³C values. Among these, the inhumed individual from Tomb IX, a female aged 16–18 years, has the lowest δ¹³C and δ¹⁵N values in the sample (δ¹³C = − 17.6‰; δ¹⁵N = 9.7‰).

In the faunal subset, both δ¹³C and δ¹⁵N values are lower than in humans, with a mean δ¹³C of − 18.1 ± 3.7‰ and a mean δ¹⁵N of 7.3 ± 1.8‰ (Supplementary Table S4). The two specimens of Gallus gallus have the highest δ¹³C values (δ¹³C = − 10.0‰ and − 10.4‰). In three herbivores, δ¹⁵N values are notably higher than the rest of the faunal dataset, exceeding 7‰ (Supplementary Figure S3).

Dietary reconstruction at CUS-Piovego

Stable isotope analysis from the inhumed individuals of the CUS-Piovego necropolis indicates a predominantly terrestrial diet characterised by limited intra-population variability and a marked reliance on C₄ plants. Contemporary measurements of foxtail millet (Setaria italica) and common millet (Panicum miliaceum) show δ¹³C values between − 13.9‰ and − 11.3‰ and between − 14.3‰ and − 12.0‰, respectively^47,48. Assuming comparable isotope values for these crops during the Iron Age in Veneto, the CUS-Piovego data strongly suggest a dietary pattern largely dominated by C₄ plants. Supporting this interpretation, in palaeodietary studies, δ¹³C values close to − 18‰ are generally interpreted as indicative of mixed C₃/C₄ dietary regimes, whereas values around − 12‰, such as those observed among the CUS-Piovego inhumed individuals, are typically associated with diets predominantly reliant on C₄ resources^49,50,51.

The trophic δ¹⁵N enrichment is approximately 3–5‰, aligning with the expected trophic shift in diets including herbivorous animals⁵². The relatively high δ¹⁵N values observed in the human sample may reflect a combination of factors, including the consumption of animal protein and elevated baseline δ¹⁵N values linked to soil ¹⁵N-enrichment from manuring practices^53,54,55,56.

The only infant in the subset shows elevated δ¹⁵N values (Tomb XI: δ¹⁵N = 13.1‰), consistent with breast-milk consumption, reflecting the approximately 2–4‰ trophic offset commonly observed in breastfed infants^45,46.

The faunal dataset from the CUS-Piovego necropolis provides an essential, albeit limited, baseline for interpreting human isotope values. Faunal δ¹³C values are generally lower than those of humans, suggesting that widespread foddering with C₄ plants was unlikely. This pattern supports the interpretation that the elevated δ¹³C values observed in humans primarily reflect direct consumption of C₄ plants. However, this pattern is not uniform across all faunal taxa. In particular, Gallus gallus specimens exhibit comparatively higher δ¹³C values, consistent with a predominantly C₄-based diet, suggesting targeted feeding practices that differ from those observed in other domestic animals^57,58.

When considered together with the pronounced δ¹³C divergence between humans and fauna, the observed trophic δ¹⁵N offset allows for multiple interpretive scenarios. One possibility is that C₄ crops – clearly forming a central component of the human diet – were cultivated on manured soils. In this regard, high δ¹⁵N values (i.e., > 7‰) observed in some herbivores may reflect grazing on manured pastures, suggesting the use of organic fertilisation strategies capable of increasing the δ¹⁵N values of both plant and animal resources^53,54,55,56. Another possibility is that the higher δ¹⁵N values reflect the consumption of poultry raised on C₄ plants. As noted above, the Gallus gallus specimens from the CUS-Piovego necropolis exhibit high δ¹³C values, consistent with a near-exclusive C₄-based diet (Fig. 2; Supplementary Figure S5), raising the possibility that human δ¹³C values may partly derive from the consumption of meat from these animals.

To contextualise this pattern, domestic fowl was introduced to Italy by at least the first half of the 9th century BCE⁵⁹. Initially appreciated mainly for their symbolic value, chickens were more commonly associated with ritual contexts than domestic ones until the 3rd century BCE, particularly in the Po Valley and Etruria^59,60,61. Their economic importance began to grow only from the 4th -3rd century BCE, as indicated by increasing evidence of breeding and dietary use⁵⁹. From the 6th century BCE onward, however, chicken appear to have played an increasingly prominent role in the diet^59,60,61. Isotope data from the CUS-Piovego necropolis may therefore offer new insights into how this relatively recent introduction was integrated and exploited within local subsistence strategies. Elevated δ¹³C values – although lower than those recorded in chickens from CUS-Piovego – have also been reported in canids from a later site in Veneto, Seminario Vescovile (3rd -1st century BCE). In this case, relatively low δ¹⁵N values have suggested that these animals were fed a C₄-based diet¹⁴.

The isotope data from the CUS-Piovego provide no evidence for a significant contribution of marine or freshwater fish to the diet^62,63. This interpretation is further supported by the archaeozoological record: despite the general scarcity of fish remains in Iron Age contexts across the Veneto region may partly reflect recovery bias, freshwater taxa are only rarely documented in both settlement and funerary contexts in Padua, including sites such as Questura/Riviera Ruzante and CUS-Piovego necropolis⁶⁴.

Despite the potential bias inherent in the assumption that the faunal assemblage adequately represents the local trophic baseline, the human isotope values are broadly consistent with the available faunal data, suggesting that the analysed domestic fauna represent at least part of the local dietary resources.

Regional and diachronic patterns of C₄ plant consumption

The data from the CUS-Piovego necropolis consistently indicate that millet was a major component in the diet of the inhumed individuals. When placed within a broader regional and chronological framework of northern Italy, these findings appear more pronounced than earlier evidence from western Veneto, where isotope data from the Middle and Late Bronze Age indicate a mixed consumption of millet and C₃ plants, partly mediated through C₄-fed animals^65,66.

C₄ plants were introduced into northeastern Italy through networks connecting the Eastern Alpine region with Danube-Carpathian agricultural sites, with the Adige River serving as a key corridor^{49,66,67,68,69}. From northern Italy, C₄ crops gradually spread southward along the so-called “Italian millet road”¹³. However, while millet consumption remained limited in central and southern Italy throughout the Bronze and Iron Ages^{65,66,70,71,72,73,74}, a different pattern emerged in northern Italy, particularly in the Po Plain. Here, rapid population growth from the Early Bronze Age, peaking in the Middle/Late Bronze Age with the rise of the Terramare culture^75,76,77, likely contributed to the increased adoption of millet as a flexible and resilient resource under conditions of demographic pressure^77,78,79. Their high yield, short growing cycle, drought tolerance, and low maintenance requirements made millets a strategic component of subsistence systems^65,66,78,80.

As a result, from the 2nd millennium BCE onward, increased δ¹³C values are recorded in the Po Plain and western Veneto, likely reflecting the increasing role of C₄ plants in local subsistence strategies^65,66,81,82. Archaeobotanical evidence further supports this interpretation, documenting the presence of both Panicum miliaceum and Setaria italica at numerous Middle and Late Bronze Age sites^83,84,85.

Similar patterns are observed across Central Europe. Numerous studies from Croatia, Slovenia, Czechia, Austria, France, Poland, and Germany confirm the widespread consumption of C₄ plants beginning in the Middle and Late Bronze Age, although their integration into local subsistence strategies varied considerably across regions^{5,7,50,51,86,87,88,89,90,91,92,93,94,95,96,97,98}.

As noted above, C₄ plant consumption was not a novelty in western Veneto; however, the human δ¹³C values at CUS-Piovego are notably higher than those previously reported for other contexts in the region⁸²(Supplementary Figure S4). Moreover, at CUS-Piovego, there is limited evidence for δ¹³C offset in the faunal sample (mean δ¹³C= − 18.1 ± 3.7‰), indicating that animal foddering with C₄ plants was not a widespread practice. This pattern, which is consistent with observations from other central European sites^5,94,95 and comparable to isotope values from other Bronze and Iron Age contexts in the region⁸², supports the interpretation that the elevated δ¹³C values in humans primarily reflect direct consumption of C₄ plants. (Supplementary Figure S5). Moreover, human δ¹⁵N values at CUS-Piovego are higher than those previously recorded in western Veneto^65,66,81,82(Supplementary Figure S6), which may suggest access to relatively protein-rich resources alongside C₄ staples.

Current isotope evidence from adult individuals from the Veneto region and adjacent areas, spanning the Early Bronze Age to the Late Iron Age⁸², shows that C₄ plants began to be consistently incorporated into human diets from the Middle Bronze Age onwards (Fig. 3). However, this process was neither uniform nor linear. Isotope data from Bronze Age sites in the northeastern part of the Peninsula, including Friuli and Istria (e.g., Sedegliano, Mereto, Monte Orcino/Určin), continue to reflect predominantly C₃-based diets^65,66, highlighting the existence of regionally variable and site-specific dietary practices. For this reason, it is important to highlight that rather than reflecting a diachronic shift or uniform regional trajectory, the available evidence points to a mosaic of local dietary practices, shaped by site-specific dynamics. Available datasets remain sparse, unevenly distributed, and often derived from socially or contextually specific subsets of the population.

Proceeding chronologically, the most substantial isotope evidence for the Early Bronze Age comes from the sites of Arano di Cellore (Verona) and Ballabio-Prato della Chiesa (Lecco). The former represents the largest Early Bronze Age necropolis known in northern Italy^99,100, while Ballabio is a rock shelter located in the Pre-Alps, dated to the final Early Bronze Age/Early Middle Bronze Age^101,102. Mean δ¹³C values in humans are − 20.2 ± 0.2‰ at Arano and − 20.4 ± 0.2‰ at Ballabio, while δ¹⁵N values average 7.9 ± 0.4‰ and 8.0 ± 0.7‰, respectively^103,104. These results suggest relatively homogeneous diets at both sites, primarily based on C₃ plant consumption, with no significant intra-population dietary variation by sex, age, or social status^103,104.

Although current data suggest that the consumption of C₄ plants during the Early Bronze Age was not widespread in northeastern or southern Italy^65,66, the available evidence remains too limited to support definitive conclusions. The spread of millets in northeastern Italy – and particularly in the Po Plain – appears as a discontinuous, site-specific process, which may have begun as early as this phase. In western Veneto, caryopses of Panicum have been recovered from the Early Bronze Age site of Canàr¹⁰⁵. Furthermore, isotope analysis of a single subadult (aged 1–2 years at death) from the pile-dwelling of Dossetto di Nogara (Verona), dated to the central phases of the late Early Bronze Age 1 (ca. 2200 − 1800 BCE), yielded a markedly enriched carbon value (δ¹³C = − 13.5‰ and δ¹⁵N = 8.5‰), consistent with C₄ plant consumption⁶⁶. While this isolated data point cannot be taken as evidence of widespread adoption, it may indicate sporadic and site-specific episodes of millet consumption, predating the more clearly attested patterns of the Middle Bronze Age in the Po Plain⁶⁶.

More robust isotope datasets are available for the Middle Bronze Age, particularly from two contemporaneous cemeteries in the Verona area: Olmo di Nogara¹⁰⁶ and Bovolone¹⁰⁷. At Olmo di Nogara, a large necropolis in the Adige Valley, mean δ¹³C and δ¹⁵N values are − 14.9 ± 1.1‰ and 9.3 ± 0.81‰, respectively, while at Bovolone, they are − 15.9 ± 2.1‰ and 8.9 ± 0.9‰^65,66. These values likely reflect the incorporation of millets into the subsistence practices of Terramare communities from the Middle Bronze Age 2 (ca. 1550 − 1500 BCE) onwards^{65,66,77,78,84}. However, when considered alongside contemporaneous evidence from northeastern Italy – where predominantly C₃-based diets are still observed – these data further emphasise the regional variability of dietary practices during this period.

Taken together, these findings suggest that what is often described as a “dietary shift” between the Early Bronze Age and the Middle Bronze Age should instead be interpreted with caution: current evidence does not support the existence of a homogeneous or linear transition. Rather, the emergence of C₄ plant consumption in northern Italy appears as a fragmented and spatially uneven process, shaped by localised social, environmental, and cultural dynamics.

While isotope data confirm that C₄ plant consumption became widespread from the beginning of the Middle Bronze Age 2^78,80, this pattern is unlikely to reflect an abrupt dietary shift. Instead, it may indicate a more gradual adoption process, potentially preceded by earlier phases of experimentation in the later stages of the Early Bronze Age, likely in response to increasing demographic pressure⁷⁷. Archaeobotanical and archaeological evidence support this interpretation, pointing to a gradual and selective southward diffusion of C₄ crops from the Carpathian-Danubian region through the Adige Valley, mediated by long-standing transalpine interactions with pile-dwelling and later Terramare communities^{49,66,67,68,69}. The widespread and socially inclusive adoption of C₄ plants in the Middle Bronze Age, as documented by isotope data⁶⁶, may thus represent the culmination of a longer, exploratory phase of agricultural experimentation^78,80. In this light, isolated Early Bronze Age communities such as Arano di Cellore and Ballabio, situated in upland contexts with limited exposure to these trans-regional dynamics, likely remained peripheral to these processes for some time.

For the Final Bronze Age/Early Iron Age, isotope data are currently available only from northwestern Italy, specifically from the site of Buco del Diavolo (Imperia, Liguria). The results indicate a diet based primarily on C₃ plants, with a mean human δ¹³C value of − 17.8 ± 1.9‰ and a mean δ¹⁵N value of 7.8 ± 0.9‰¹³. Despite the limited sample size from this period constraining the extent to which regional dietary patterns can be comprehensively assessed, the isotope data from Buco del Diavolo nonetheless stand in clear contrast to those recorded for Middle Bronze Age populations in the western Veneto. As noted above, the absence of C₄ plant isotopic signatures in the Ligurian assemblage underscores the geographically restricted nature of millet consumption, which appears to have been typical of the western Veneto⁸².

Isotope data from the later necropolis of Seminario Vescovile (3rd -1st century BCE) indicate an increasing importance of C₄ plants in the diet – estimated to contribute over 40% of daily caloric intake – within a framework of greater isotopic variability, a pattern that will be discussed in more detail below¹². This spatial divergence in dietary practices likely reflects that dietary choices were shaped by the interplay of local environmental conditions, agricultural systems, and culturally mediated food preferences, underscoring the complexity and regional variability of subsistence strategies across northern Italy during the period.

Diet, mobility and social implications

The isotope data obtained in this study indicate a substantial contribution of C₄ plants to the diet of the inhumed individuals, consistent with a mixed dietary regime centred on C₄ cereals and complemented by animal protein. Stable isotope evidence from Bronze and Iron Age Central European sites indicates that millet consumption was frequently associated with individuals of lower social status, suggesting that social inequalities were expressed not only through funerary practices but also through differential access to food resources^{5,6,7,62,86,92,93,108}. This association persisted into later periods, as millet is attested in both the archaeological record and written sources throughout the Roman Empire, where it was generally regarded as a low-status crop, primarily consumed by the poor or used as livestock fodder^109,110.

Accordingly, the prominent contribution of millet observed in the inhumed individuals from the CUS-Piovego necropolis could be consistent with a dietary pattern that may be associated with lower social status. Evidence from Iron Age Veneto further supports this association. Gas chromatography–mass spectrometry (GC–MS) analyses of ceramic vessels’ residues from the site of Questura/Riviera Ruzante in Padua, a metallurgical workshop calibrated radiocarbon dated to the late-final 9th century BCE, have revealed a predominance of C₄ plant biomarkers, indicating the consumption of millet-based products such as porridges or fermented beverages like millet beer¹⁰⁸. In particular, miliacin, i.e., the specific biomarker for Panicum miliaceum^111,112,113 was frequently detected, suggesting that millet was used either in boiled soups or for brewing¹⁰⁸. As the site was associated with metallurgical production, these individuals were likely craft specialists – perhaps temporarily hosted in the urban premises where they consumed their own food – and generally considered to belong to lower-status segments of society¹¹⁴.

This interpretation gains additional support when considered alongside the funerary context of Iron Age Veneto, where inhumation has been interpreted as potentially associated with individuals of lower or socially distinct status. In particular, at the CUS-Piovego necropolis this interpretation is supported by several archaeological observations: (1) inhumation represents a minority rite within the necropolis, in contrast to the predominance of cremation practices, and may also reflect a less resource-intensive funerary treatment; (2) inhumed individuals are generally characterised by an almost complete absence of grave goods, whereas cremation burials are more frequently associated with assemblages that can include elaborate and potentially high-status objects; and (3) the presence of atypical inhumations, such as the potentially bound individual (i.e., Tomb IX) and the human–horse co-burial (i.e., Tomb UFC 12), has been interpreted as suggestive of forms of social differentiation and/or ritualised killing^22,23,26.

However, although the isotope data from the inhumed individuals at CUS-Piovego are consistent with a dietary pattern that may be associated with lower social status, in the absence of comparative data from cremated individuals, the relationship between millet consumption and social status remains indirect and should be considered suggestive rather than definitive. Moreover, the role of millet consumption is inherently complex and may vary depending on environmental conditions, agricultural strategies, and cultural practices.

Recent archaeobotanical evidence from the Horn of Africa shows that between ca. 1000 BCE and 1000 CE C₄ plants – such as t’ef, sorghum, and finger millet – formed part of diverse, mixed subsistence systems involving both wild and domesticated resources, rather than reflecting a single socio-economic pattern¹¹⁵. Similarly, evidence from Eastern Sudan indicates that from the 2nd millennium BCE onwards, increasing aridity led to a reorganisation of subsistence strategies, with a growing reliance on drought-resistant C₄ crops, highlighting their role as adaptive responses to environmental change¹¹⁶. Furthermore, evidence from Neolithic China highlights a strong integration of millet agriculture and animal husbandry, in which millet served as both a staple food and a primary fodder resource⁵⁷.

Taken together, these examples demonstrate that C₄ plant consumption cannot be straightforwardly interpreted as an indicator of low social status, as it may instead reflect a range of environmental, economic, and cultural factors. Moreover, elevated δ¹³C values in humans may derive from multiple pathways, including the consumption of animals raised on C₄-based diets, thereby complicating any direct link between millet consumption and social implications.

At the same time, the elevated δ¹⁵N values observed in the CUS-Piovego sample may reflect a higher intake of animal protein, which has elsewhere been associated with individuals of higher social role^117,118,119. However, within the broader archaeological and isotopic context of the CUS-Piovego, these values are more plausibly explained by baseline enrichment linked to manuring practices or by the consumption of animals, such as domestic fowl, raised on isotopically enriched diets. Given the equifinality of bulk collagen isotope data, these alternative pathways cannot be disentangled, and any interpretation linking δ¹⁵N values directly to social differentiation should therefore be treated with caution.

The dataset from the CUS-Piovego necropolis indicates a relatively homogeneous dietary pattern, with no apparent sex differences (Fig. 2). However, as noted above, this observation cannot be statistically tested due to the limited number of individuals. Nevertheless, four adult females (the inhumed individuals from Tombs I, IV, IX, and XX) exhibit slightly lower δ¹³C values (Supplementary Table S3). Notably, previously published ⁸⁷Sr/⁸⁶Sr isotope data²² identified three of these females (the inhumed individuals from Tombs I, IV, and IX) as non-local/mobile. The comparatively lower δ¹³C values of these females may therefore reflect dietary practices adopted in the years before their arrival in the Padua area. As rib collagen reflects dietary intake over the last few years before death¹²⁰, these values could retain an isotope signal formed elsewhere, before the full incorporation of a local C₄-based dietary signature. Similar patterns have been observed in other Iron Age contexts, where correlations between δ¹³C values and ⁸⁷Sr/⁸⁶Sr ratios suggest that dietary variability may be partly influenced by geographic origin¹²¹.

Among these individuals, the case of Tomb IX is of particular interest. The integration of archaeological and multi-isotope data for the young female from this burial offers valuable insights into her life history. Although no skeletal evidence of trauma or physiological stress was identified, the funerary context is highly atypical. The prone position, with the upper limbs placed behind the back and the lower limbs flexed and slightly elevated relative to the rest of the body, represents a non-physiological arrangement that strongly suggests the use of restraint, likely through binding of the limbs. This unusual treatment, combined with the absence of grave goods and the broader funerary context of inhumation at CUS-Piovego, has been interpreted as indicative of marginalisation, raising the possibility that the individual was a war captive or an enslaved person, potentially executed or ritually killed²².

From a bioanthropological perspective, the individual has been identified as a young female, with an estimated age at death of 16–18 years based on standard osteological and dental indicators (see Materials and Methods). The osteological sex estimate was further confirmed through palaeoproteomic analysis of amelogenin in tooth enamel (Supplementary Figure S1).

Isotopically, this individual stands out as a clear outlier in both dietary and mobility profiles. She exhibits the lowest δ¹³C (− 17.6‰) and δ¹⁵N (9.7‰) values in the sample (Fig. 3), consistent with a diet poor in animal protein, predominantly based on C₃ plants, and with minimal or absent consumption of C₄ resources compared to other individuals (Figs. 2 and 3). These values differ markedly from those observed in western Veneto⁸², suggesting that her isotopic signature does not reflect local dietary patterns. Given that rib collagen reflects relatively short-term dietary intake¹²⁰, these values likely retain a signal formed elsewhere, prior to her arrival in the Padua area. This interpretation is further supported by strontium (⁸⁷Sr/⁸⁶Sr) isotope data, which identify her as non-local and suggest a probable origin in the northeastern Alpine region, based on the Italian isoscape^22,122.

Taken together, the combined archaeological, proteomic, bioarchaeological, and isotope evidence for the young female from Tomb IX points to a life history characterised by mobility and social marginalisation. The apparent mismatch between her dietary signature and the local isotopic baseline suggests that she spent only a limited period in Padua before death. While these interpretations remain necessarily cautious, this case highlights the value of integrating funerary and multi-isotope data in reconstructing individual life trajectories.

Future application of histologically driven spatially resolved ⁸⁷Sr/⁸⁶Sr isotope analysis [e.g., LA-ICP(MC)MS] could further refine the timing and dynamics of her mobility, offering high-resolution insights into patterns of movement during the final years of life^123,124.

While the case of the inhumed from Tomb IX highlights individual variability within the necropolis, a broader interpretation of the isotope data from CUS-Piovego requires caution. Burial treatment alone does not provide unambiguous evidence of social marginalisation, and the interpretation of atypical inhumation practices in social terms remains necessarily inferential. In addition, interpreting the pronounced C₄ signal at CUS-Piovego as indicative of a widespread dietary change in the Middle Iron Age would be misleading, as it likely reflects the practices of a specific subgroup rather than a regional trend. To date, the isotope data from CUS-Piovego remain the only dataset available for this period in western Veneto and are exclusively derived from inhumed individuals. These individuals likely represent a socially distinct subgroup, whose isotope values – characterised by overall homogeneity and limited dietary variability – should be understood not as representative of the broader community but rather as indicative of their particular social positioning within the local context.

This interpretation becomes clearer when compared with the isotope evidence from the later necropolis of Seminario Vescovile (3rd -1st century BCE), which presents a markedly different picture. While indicating a substantial contribution of C₄ plants to the diet, the human remains display a much broader isotopic range¹⁴. This higher variability likely reflects the dietary diversity of a larger, more socially stratified population, associated with the Cenomani Gauls and increasingly influenced by Roman cultural practices. In contrast to the limited variability observed among the inhumed individuals from CUS-Piovego, this comparison underscores the importance of contextualising isotope data: the homogeneity observed at CUS-Piovego likely pertains to a socially specific subgroup and should not be taken to represent regional dietary patterns in the Iron Age more broadly.

Taken together, the results from CUS-Piovego necropolis highlight the importance of integrating isotope evidence with archaeological context when exploring the complex relationship between diet, mobility, and social differentiation in past societies.

At the CUS-Piovego necropolis of Padua, the coexistence of cremation and inhumation rites reflects complex social dynamics during the Middle Iron Age. Based on funerary evidence, inhumation has been archaeologically interpreted as a rite associated with socially marginal or distinct individuals, suggesting possible differentiation in funerary treatment and lived experience. By integrating stable isotope analysis with funerary evidence, this study contributes to ongoing discussions on how dietary practices relate to subsistence strategies and social identity within the broader context of emerging urbanisation in Iron Age Veneto.

Despite the lack of comparative isotope data from cremated individuals, δ¹³C and δ¹⁵N data from the inhumed indicate a predominantly terrestrial-based diet, with a notable reliance on C₄ plants. This pattern suggests limited dietary diversity, potentially supporting interpretations of social marginalisation, although alternative explanations cannot be excluded.

The case of the young female from Tomb IX – whose atypical burial and isotope values deviate from the broader dataset – highlights possible links between mobility, diet, and funerary treatment, illustrating variability in individual life histories within the community.

Overall, these findings point to heterogeneity in lived experiences, with social differences potentially expressed through funerary practices. However, such interpretations require caution, as neither burial treatment nor isotope data alone can unequivocally define social status.

This research underscores the value of a multidisciplinary approach in reconstructing past social structures, showing how the integration of bioarchaeological and archaeological data can refine interpretations of social organisation. Further research should expand the local isotopic baseline to support the application of quantitative approaches, including Bayesian mixing models, and extend palaeodietary and mobility analyses to other Iron Age contexts in northern Italy. This will help determine whether the patterns observed at CUS-Piovego reflect local dynamics or broader regional trends associated with urbanisation, mobility, and social organisation during the 1st millennium BCE.

The human and faunal sample

The skeletal remains from the CUS-Piovego necropolis are currently housed at the Archaeology Laboratories of the University of Padua and at the Musei Civici of Padua, Italy. Due to preservation of their skeletal remains, only 19 of the 26 identified inhumed individuals from the CUS-Piovego necropolis were selected for stable isotope analysis. The sample comprises 17 adults (> 20 years at death), one late adolescent (the inhumed from Tomb IX, aged between 16 and 18 years), and one infant (the inhumed from Tomb XI, aged around 1.5 years) (Supplementary Table S1).

Age-at-death estimation for adults was based on the following criteria: (a) tooth wear patterns in the permanent dentition¹²⁵, (b) degenerative changes in the sternal rib epiphysis^126,127, (c) and degenerative changes in the symphyseal surface of the pubic symphysis¹²⁸, and (d) and degenerative changes in the auricular surface of the ilium¹²⁹. For subadults, age-at-death was estimated using: (a) the stage of formation and eruption of primary and permanent dentitions¹³⁰, (b) the developmental and growth stages of long bones¹³¹, and (c) the assessment of epiphyseal closures¹³¹.

Sex estimation in adults was conducted through the examination of sexually dimorphic traits in the skull and pelvis^132,133. The biological sex of subadults was determined via proteomic analysis of sex-specific amelogenin peptides in dental enamel^134,135,136(see Supplementary Figure S1).

To establish the δ¹³C and δ¹⁵N isotope baseline, 16 faunal bone samples from the CUS-Piovego site were analysed (Supplementary Table S2). The assemblage comprises Equus caballus (n = 3), Sus domesticus (n = 3), Bos taurus (n = 2), Ovis aries (n = 2), Capra hircus (n = 2), and Gallus gallus (n = 2) (Supplementary Table S2). The Equus caballus specimens derive from horse burials^30,137, whereas the remaining elements were recovered from cremation burials and should be interpreted as meat offerings associated with funerary rituals (Supplementary Table S2). Whilst it cannot be assumed that these samples are directly representative of meat consumed by the humans in this study, they are contemporaneous and therefore provide valuable indications of the local food chain isotope variation. The standards used for taxonomic identification, as well as for sex and age-at-death estimation, are detailed in Supplementary Information.

Sex-specific amelogenin peptides analysis in subadults

Enamel peptide analysis was carried out at the MeGic Lab, Department of Geological and Chemical Sciences, University of Modena and Reggio Emilia, Italy. Approximately 5 mg of enamel was sampled from an upper right first permanent molar, using a flexible diamond-edged rotary wheel, mounted on a DREMEL model 300¹³⁴. Samples were demineralised with 200 µL of 1.2 M HCl at room temperature for 45 min. The first batch of acid was discarded before the actual extraction. The supernatant containing both minerals and peptides was transferred to a new Eppendorf tube. The samples were thus desalted and purified using in-house STAGE-tips with C18 functionalised silica. Resin-bound peptides were eluted using 20 µL of 60% acetonitrile in 0.1% formic acid. Finally, the samples were dried at room temperature under a laminar flow hood (class 100). Dry extracted peptides were resuspended in 35 µL of a mixture of water: acetonitrile: formic acid 95:3:2, before the nLC-MS/MS measures. The analysis was conducted using Nano UHPLC Ultimate 3000 coupled to an Exploris™ 480 Hybrid Quadrupole-Orbitrap™ Mass Spectrometer via an EASY-Spray source interface, housed at the Centro Interdipartimentale Grandi Strumenti of the Department of Geological and Chemical Sciences, University of Modena and Reggio Emilia, Italy [more details in 135].

The ion chromatogram was searched using Xcalibur (Thermo Scientific) with a mass tolerance of 5 ppm. We specifically focused on peptides SM(ox)IRPPY (AMELY; [M + 2 H]²⁺ 440.2233 m/z), SIRPPYPSY (AMELX; [M + 2 H]²⁺ 540.2796 m/z) and (AMELY; [M + 2 H]²⁺ 396.7073 m/z), demonstrated to be strong sex biomarkers^134,138,139(Supplementary Figure S1).

δ¹³C and δ¹⁵N in human and animal bone collagen

Collagen extraction was undertaken at Cardiff University BioArchaeology Labs, following the Longin protocol¹⁴⁰, modified according to Brown and colleagues¹⁴¹. The atomic C: N ratio (C: N_a) and the collagen yield of each sample were recorded to check collagen quality. Extracts with C: N_a ratios ranging from 2.9 to 3.6, indicating acceptable collagen quality, although overall preservation was variable and, in several cases, marginal due to low collagen yields^42,43,142. The surface of the bone was abraded with a diamond-coated burr, and then samples were extracted using a rotary diamond wheel. Extracted bone samples weighed approximately 500 mg. Samples were demineralised in 0.5 M HCl until soft, then rinsed with deionised water and gelatinised in pH 3 H₂O (acidified with HCl) on a hot block at 75 °C. After 48 h, samples were removed from the hot block, filtered using Ezee™ filters, transferred to polypropylene test tubes, and frozen overnight. Samples were then lyophilised, leaving dry gelatinised collagen.

Collagen samples were measured using a Thermo Flash EA 1112 series elemental analyser connected to a Conflo III and Thermo Delta V Advantage mass spectrometer in the School of Earth and Environmental Sciences at Cardiff University. Results for δ¹³C and δ¹⁵N are reported in the δ notation as permil (‰) relative to Vienna-Pee Dee Belemnite (VPDB) and Air, respectively.

Samples were analysed in combination with in-house standards, which are calibrated against international standards IAEA-600 (δ¹³C = − 27.771‰ and δ¹⁵N = 1.0‰), IAEA-CH-6 (δ¹³C = − 10.449‰), and IAEA-N2 (δ¹⁵N = 20.41‰). In-house standards included a lab-grade caffeine [δ¹³C = − 33.30‰, δ¹⁵N = -1.4‰] and two commercial collagen food supplements [MarCol (δ¹³C = − 16.20‰, δ¹⁵N = 14.36) and MCF (δ¹³C = − 22.36‰, δ¹⁵N = 4.26‰)]. Caffeine and MarCol were used for sample-size correction and two-point normalisation, while all three were used as check-standards. Analytical precision is expressed as the combined standard deviation s of all check standards during the analytical period, with values s = 0.05‰ and s = 0.09‰ for δ¹³C and δ¹⁵N, respectively (N = 44).

Statistical analysis

Statistical analysis and data visualisation were performed using the R environment for statistical computing (version 4.5.3)¹⁴³.