A recent analysis of eleven bronze artifacts from central Italy offers detailed insights into the metalworking traditions of the Roman and early medieval periods. Ranging from everyday tools to ornamental items, these objects show how ancient metallurgists adapted copper alloys for specific structural needs. The research was published in the journal Archaeological and Anthropological Sciences.
The artifacts originate from two distinct archaeological sites in the municipality of Civitella d’Agliano, located in the Middle Tiber Valley. The first location is a large Roman cistern at the site of Spoletino, originally excavated into natural clay layers. Built in the late Republican period, this water reservoir served a surrounding villa dedicated to the intensive agricultural exploitation of the local landscape. The surrounding estates regularly produced crops along with bricks and tiles destined for the markets of Rome, utilizing the Tiber River as a direct transportation route. A wall divided the cistern in the middle of the first century, and by the fourth century, the structure was abandoned and filled with construction debris and discarded household items.
The second site is the necropolis of Castel Sozzio, an early medieval cemetery used between the fifth and seventh centuries. It currently represents the only systematically documented funerary site in the immediate region. Archaeologists study rural settlements like these to understand how ordinary people managed their physical resources outside major urban centers. Questions persist regarding the degree of technical knowledge these local metalworkers possessed. Analyzing the exact chemical combinations of everyday tools helps reveal the practical skills and resource networks available to agricultural and valley communities in central Italy.
The study was led by Tilde de Caro of the Institute for the Study of Nanostructured Materials at Italy’s National Research Council, alongside a team of specialists from Sapienza University of Rome and Roma Tre University. The researchers examined a total of eleven bronze items, including fragments of plaques, needles, hatpins, a fishing hook, and a hinge. Four of the artifacts were selected for internal cross-section analysis, which required cutting them open to observe the uncorroded metal layers deep inside. The analytical process combined visual inspection with structural chemistry to capture a complete picture of the samples.
The team used optical microscopy to document the colors and physical textures of the surface layers, known as patinas. They applied scanning electron microscopy with energy-dispersive X-ray spectroscopy to measure the specific elemental composition of both the metal cores and the corroded edges. This technique involves directing a beam of electrons at the sample, which causes the material to emit X-rays that form a specific signature for each chemical element present.
To identify exactly what minerals had formed over centuries of burial, the researchers used micro-Raman spectroscopy. This technique focuses a laser onto the artifact, and the resulting light scatter provides a fingerprint of the molecular bonds in the corrosion products. Finally, the researchers used electrochemical impedance spectroscopy to evaluate the current preservation state of the artifacts. This non-destructive method passes a mild alternating electrical current through the object to measure its electrical resistance, which allows scientists to estimate how effectively the patina protects the object from further decay.
The physical testing revealed a deliberate technological logic behind the ancient metalworking practices in the valley. The artifacts are composed of two main types of bronze alloys: a binary mix of copper and tin, and a ternary blend containing copper, tin, and lead. The makers used the binary copper-tin alloy for objects that required a high degree of hardness, such as needles and hatpins. For objects that demanded easier casting and shaping, such as thick plaques, they incorporated lead to create the ternary alloy. Lead improves the flow and workability of molten metal but tends to pool into tiny globules as the metal cools, creating specific microstructures inside the bronze.
Trace amounts of zinc were also found in some materials, pointing to the origins of the raw materials. Its presence suggests the bronze makers occasionally sourced unrefined copper ores from zinc-rich mines or melted down and recycled older metal scraps that contained impurities. Over hundreds of years underground, these metallic blends interacted with the local soil to produce varying patterns of decay. A common process known as decuprification occurred on several items, where the copper dissolved into the soil faster than the other elements, leaving a brittle, tin-heavy layer at the surface.
The chemical patterns left on the artifacts also reconstruct the physical environment where they rested for centuries. The patinas on several items contain lazurite, a mineral that forms under sulfur-rich conditions. Its presence indicates that those specific items interacted heavily with decomposing organic matter, likely human remains in the necropolis or dense layers of decaying plant material inside the abandoned cistern. Other surfaces feature phosgenite, a mineral that forms when lead interacts with chlorine and carbon dioxide in the surrounding soil.
Despite these varied chemical interactions, the electrochemical testing showed that the objects are corroding at an exceptionally slow rate, estimated at between zero and 0.1 millimeters per year. The soils in the Middle Tiber Valley proved to be fairly mild, allowing the bronze objects to form stable, protective oxide crusts that insulated their metallic cores. Copper oxides like cuprite and copper carbonates like malachite formed dense barriers on the surface, largely preventing moisture and oxygen from reaching the intact metal beneath.
The study faced several technical limits regarding the reconstruction of ancient corrosion. Electrochemical measurements conducted in a laboratory rely on short-term current applications in artificial liquid solutions, which might not entirely replicate the complex, fluctuating soil densities that an artifact experiences over hundreds of years. The sample size of eleven items also restricts broad conclusions about the entire region’s metal economy during late antiquity. Since most of the intact objects were delicate, deep cross-sectional analysis was limited to only four fragments to preserve the physical integrity of the other artifacts.
Future archaeological excavations in the Middle Tiber Valley region could expand this dataset by yielding more tools and ornaments from adjacent residential zones. Mapping out more grave sites at Castel Sozzio would provide a larger sample of medieval metalwork for direct comparison to the older Roman materials. Identifying the specific mineral signatures on these bronzes offers conservators a clear baseline for selecting appropriate chemical treatments to neutralize active decay in existing collections. Understanding exactly how the soils of central Italy interact with copper alloys will guide future preservation efforts for artifacts that still lie undiscovered beneath the agricultural fields.
The paper, “Roman and Early Medieval bronze artifacts from the Middle Tiber Valley: Technological and conservation insight through optical microscopy, Raman spectroscopy, SEM-EDS, and electrochemical analysis,” was authored by Tilde de Caro, Andreea Lazaroiu, Emanuela Borgia, Marcello Spanu, Mara Elefante, Andrea Macchia, Francesca Irene Barbaccia, Martina Bernabale, and Caterina De Vito.