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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

Reviewer #1: Yes

Reviewer #2: Yes

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2. Has the statistical analysis been performed appropriately and rigorously? -->?>

Reviewer #1: Yes

Reviewer #2: Yes

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3. Have the authors made all data underlying the findings in their manuscript fully available??>

The PLOS Data policy

Reviewer #1: Yes

Reviewer #2: Yes

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4. Is the manuscript presented in an intelligible fashion and written in standard English??>

Reviewer #1: Yes

Reviewer #2: Yes

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Reviewer #1: “Tracing Socioeconomic Change and Emerging and her colleagues Elites in 4th–3rd Century BCE: Metalwork from the Amber Road Corridor” by Danielisová is a well written, well organized, well-reasoned, and very data rich study. As such, in my opinion, it certainly deserves to be published by PLOS One.

I feel that the text and data are exemplary. My only criticism lies within the data presentation graphics. Such large data set are a blessing in the richness of the interpretations that can be extracted. However, they are a curse in terms of presenting them clearly. In general, too much information is being conveyed in figures that are too few and too small. This is particularly true for figures 4-8 and 12. These need to be reworked, and subdivided, and both data points and labels enlarged. I have outlined specific graphic related issues below.

Fig. 4 - It is not clear from the figure alone, what the apices represent. I suggest replacing the true labels (e.g. Co+Ni) rather than L, T, R, which are not intuitive. Also figures should be labelled with wt% rather than just %. What is the difference between the 2nd and 3rd plots, both are labelled as 3rd cent, BCE and have the same legend.

Fig. 5. – Having the same color and symbol scheme for completely different variables in A and B is initially misleading. Different symbols/colors should be used between them. There is simply too many groups plotted in 5C and 5D for the reader to readily see and interpret the patterns. Perhaps they should be split into two each (C: one for Bohemia and one for Moravia). I am not sure how to split D, but at the very least the time periods should be in sequence and one should be able to readily distinguish the similar time periods (e.g. LtB2, B2a, B2b should share a color or symbol).

Fig. 6 – Again too many data points in 5C f9r easy reading. Perhaps split into Boh sites and Mor sites

Fig 8. I had to zoom in on the image extensively to distinguish between groups, and this is made worse by the number of colors used. Break the plot into subplots with fewer sites in each. Note, the following Figs 9, 10, 11, 12 in S3 conveyed far more information to me than the summative figure 8.

Fig. 12 Text is two small to read on X-axis labels. Pb% legend should be inserted into figure.

Lines 247-248 : “the latter showing a tendency toward a more homogeneous pattern which is more evident towards the 3rd century BCE (Fig. 5.B, Fig. 7.A), especially in phases LT B2b-C1 and LT C1 (Fig. 5.D).” I do not see this in the figures. In 7A, Bohemia appears more clustered with the exception of two outliers, and 5B does not distinguish between Moravian and Bohemian artifacts.

Line 259: “The most marked differences are visible among the regions (Fig 6.A)” . I do not see any variation in clustering between the two localities.

Reviewer #2: The authors argue that during the 4th–3rd centuries BCE in Central Europe, there was a diachronic shift from heterogeneous, locally mediated copper-alloying practices to a highly standardized mass production of ‘leaded bronze’. Crucially, the authors claim that this innovation was first adopted by rural communities (visible in cemetery contexts) and only later scaled up by large open agglomeration sites like Němčice nad Hanou. Additionally, their provenance analysis suggests that the raw material (lead) for this surge in production was sourced predominantly from Transalpine Variscan deposits (like the Harz Mountains and Rhenish Massif) rather than Mediterranean imports. Finally, they connect this technological shift to the emergence of ‘bulk luxury’ goods (the voluminous ‘Plastic-Style’ jewellery) that helped form new socio-economic elite configurations.

These claims are highly significant for Iron Age archaeology. The prevailing narrative often assumes a ‘top-down’ model where centralized, wealthy agglomeration sites drove technological and economic innovation before it trickled down to rural areas. This study turns that model on its head, using hard archaeometry to position rural communities as the initial agents of change.

The authors place their findings directly within current debates regarding Iron Age centralization, socio-economic complexity, and technological transitions. They appropriately cite existing literature on Central European agglomeration sites (e.g., Roseldorf, Haselbach, Němčice) and artistic developments like the ‘Plastic-Style’. The literature on lead isotope provenance (e.g., OXALID, GlobaLID) is also treated robustly and fairly utilized.

The data and analyses strongly support the claims. The authors analysed a substantial dataset of 399 samples. Their chronological cross-section effectively demonstrates the shift: 1) Principal Component Analysis (PCA) and trace element ternary graphs clearly show 4th-century alloys were highly dispersed, while 3rd-century alloys tightly clustered. 2) The comparison between early 3rd-century rural graves and later agglomeration materials supports the timeline of rural-first adoption. 3) Isotopic Kernel Density Estimation modelling validates the narrowing of supply chains to specific geological signatures. No additional primary data is required, as the analytical pipeline is exhaustive.

The authors utilize custom pipelines for non-parametric statistical evaluation (Kernel Density Estimations) and multivariate analysis (PCA, K-means clustering). They have adhered to PLOS One's best practices by stating that all individual statistical codes (RStudio and Python) are available in the Supplementary Information 5 (S5 Text). Additionally, they compiled a 12,741-sample lead isotope database (LIDOF), which they appropriately provide in S4 Table.

The manuscript appears highly suitable for publication in its current form, pending only standard peer-review revisions.

The authors explicitly state that ‘All relevant data are within the manuscript and its Supporting Information files,’ fulfilling repository requirements for this type of dataset.

The methodology is described with sufficient technical precision. The authors detail their sampling technique (extracting 30-50 mg from the uncorroded metal core) and instrumentation (NEPTUNE Plus MC-ICP-MS and standard ICP-MS). They also provide exact algorithmic parameters for their computational modelling, such as the predefined integration ranges for isotopic values (±0.01 for ²⁰⁶Pb/²⁰⁴Pb and ²⁰⁷Pb/²⁰⁴Pb, ±0.03 for ²⁰⁸Pb/²⁰⁴Pb) and the 10% probability threshold used for KDE filtering.

The custom R and Python scripts used for evaluating the dataset are provided in the supplementary file "S5 Text".

The manuscript is logically organized and written in excellent English. While sections of the text (like the isotopic provenance analysis and PCA data structuring) are dense and highly technical, the authors do a good job in the Introduction and Discussion sections translating these geochemical findings into clear, accessible socio-economic and historical implications that a general archaeologist can understand.

Finally, I have two queries intended to help the authors expand their Discussion section, encouraging them to complement their strong archaeometric analysis with a more explicit anthropological and socio‑economic framing:

1) Comparing funerary (use/deposition) vs. agglomeration (manufacture) contexts: The study effectively contrasts 69 samples from the open industrial agglomeration at Němčice nad Hanou with samples from rural flat cemeteries. However, this compares two distinct behavioral spheres: ritualized use-deposition (curated grave goods) versus daily settlement/manufacturing discard. Could the observed shift toward standardized leaded bronzes in the 3rd-century BCE cemeteries partly reflect a cultural or ritual preference for burying specific types of objects (e.g., the voluminous 'Plastic-Style' jewelry), rather than a complete picture of the communities' daily metallurgical reality? The authors should discuss more explicitly how the taphonomic and socio-economic behaviors unique to funerary deposition versus industrial production might mediate these isotopic and chemical signals.

2) The socio-economic model, ‘warrior elites’, and amber: The authors propose a compelling socio-economic model regarding the emergence of ‘bulk luxury’ commodities, attributing the coordination of this economy to ‘local warrior elites’. However, the specific mechanisms of this control remain somewhat abstract. Could the authors clarify the role of these elites in relation to the metallurgical specialists? Were these artisans attached directly to elite households, or were they independent specialists operating within community networks? Furthermore, given that the paper is titled 'Metalwork from the Amber Road Corridor', the actual socio-economic integration of amber is underexplored in the text. While sapropelite and glass are effectively used as analogies for bulk luxuries, how did the north-south flow of Baltic amber specifically articulate with the east-west/north-south flows of Rhenohercynian lead and Alpine/Carpathian copper?

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Tracing Socioeconomic Change and Emerging Elites in 4th–3rd Century BCE: Metalwork from the Amber Road Corridor

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Dear Dr. Danielisová,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

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