Thuburbo Majus lies roughly sixty kilometers southwest of Tunis, near the modern town of El Fahs, in a fertile agricultural zone that helped the city flourish from the first through the seventh centuries CE. Granted civic status probably under Augustus and later elevated to the rank of honorary colony under Commodus in 188 CE, the city accumulated temples, a forum, a Capitolium and public baths. The Winter Baths, covering approximately 1,600 square meters in the urban core, grew through an asymmetrical layout born of repeated additions and renovations. An inscription studied in earlier scholarship allowed archaeologists to attribute the original construction to the first half of the third century CE, with major restoration phases in the late fourth to early fifth centuries and again in the early sixth century, before the building’s eventual abandonment.

The research team, led by Aida Zaddem and Karima Zoghlami with colleagues including Rafael Fort of the Institute of Geosciences in Madrid, sampled nine distinct stone lithotypes and thirty-two mortar specimens from walls across the complex. Petrographic thin sections, stained to distinguish calcite from dolomite, revealed the full petrographic identity of each rock: a nummulite-rich Oligocene packstone, travertine, ferriferous recrystallized micrite, a dense Jurassic limestone marketed even today as Aziza-type marble, a porous bioclastic calcarenite, speleothem calcite, an Eocene biomicrite, a Jurassic pelsparite and a glauconitic grainstone. Each of these was matched to a specific architectural role, and the match turned out to be strikingly deliberate.

The analysis exposed a procurement strategy of remarkable economy and precision. Nummulitic limestone and travertine, quarried within a radius of less than twenty kilometers, formed the monumental framework, minimizing transport costs while providing the mechanical strength the main structures required. The heating system told an even sharper story. The vault of the main furnace, the praefurnium, was built exclusively of fired bricks bonded with cocciopesto mortar, a technical imperative given that flames there could reach between 800 and 1,000 degrees Celsius, hot enough to decarbonate and disintegrate any carbonate stone. Yet the support pillars and the cheeks of the flue channels, made of glauconitic limestone and ferriferous micrite, remained intact, demonstrating that builders understood empirically that temperatures at those positions stayed below the limestone destruction threshold of roughly 600 to 800 degrees.

Specialization extended to the prestigious elements. Highly porous calcarenite, with porosity reaching 25 to 27 percent, was reserved for arches and voussoirs where lightness mattered, while marbles were chosen for columns, where hardness and visual prestige dominated. The mortars, meanwhile, fell into two great families: lime-based and gypsum-based. The lime mortars split into three subgroups that map directly onto Roman hydraulic science. The first type, moderately hydraulic, mixed a lime binder with siliceous and carbonate aggregates likely drawn from the sands of the nearby Oued Miliane and Oued Medjerda rivers; their hydraulicity came from clay impurities in marly limestone calcined into the binder itself, forming calcium silicate and aluminate hydrates without any added ceramics.

The second type was entirely different in purpose: non-hydraulic air-lime coatings built in multiple layers, their aggregates composed of crushed marble and vein calcite, with grain size progressively decreasing from the wall inward toward the finished surface. These white to beige plasters carried the highest calcium oxide contents of the entire assemblage, averaging around 57 percent, and their chemistry shows almost no silica, alumina or iron, confirming a purely aerial binder. Fascinatingly, one intermediate layer in some samples shows a faint reddish hue and weak hydraulic character, hinting that builders may have sprinkled finely ground ceramic powder, an artificial pozzolana, into that single stratum to fine-tune its properties. This kind of marble-dust coating echoes the plaster recipes that Vitruvius described for polished wall finishes.

The third lime type is the showpiece: highly hydraulic cocciopesto, loaded with ceramic fragments up to a centimeter across, used to waterproof the frigidarium pool and a decantation basin. Thermal analysis sealed the classification. The ratio of carbon dioxide to water lost during heating, a standard proxy for hydraulicity, dropped below 5 percent for these mortars, the signature of strongly hydraulic systems in which pozzolanic reactions between lime and fired clay generate abundant calcium silicate hydrates. Trace elements told the same story from another angle: cocciopesto samples carried the highest concentrations of niobium, rubidium, zirconium, zinc, chromium and vanadium, the geochemical fingerprint of silicate-rich ceramic aggregate. A fourth family of gypsum-based mortars, dominated by sulfate phases with sulfur trioxide averaging over 63 percent, came from the abandonment phase, when builders opportunistically exploited abundant local Triassic gypsum deposits even in structural roles that gypsum was traditionally never asked to play.

Perhaps the most consequential findings are chronological. Mortar fingerprinting forced a re-evaluation of the building’s accepted construction sequence. A joint mortar from the latrines, previously assigned to the first renovation phase of the late fourth century, proved compositionally indistinguishable from the original third-century mortars, raising the possibility that the latrines were part of the initial design and only internally modified later. A coating from the corridor wall, attributed to the original phase on architectural grounds, instead matches the crushed-marble plasters of the late-fourth-century renovation. Most strikingly, the bottom of the decantation basin, built with original-phase cocciopesto, contrasts with its upper walls of gypsum-bonded rubble, suggesting the basin’s base belongs to the first construction campaign while its upper portion was added during abandonment, a functional repurposing of the water system. The authors caution that these reinterpretations remain preliminary until confirmed by absolute dating methods such as optically stimulated luminescence or isotopic analysis.

The study also carries a warning for conservation. Soluble salts, including halite, syngenite and secondary gypsum, pervade the mortars. The gypsum largely results from the dissolution and recrystallization of older gypsum binders migrating through the masonry; the halite, at an inland site, most likely rose capillary-ward from saline groundwater or came from unwashed, evaporite-rich local sands; and syngenite forms when gypsum reacts with potassium from atmospheric deposition or fertilizers. These salts crystallize and swell with humidity, and their behavior directly explains the poor state of preservation visible across the complex today. Any modern repair mortar that ignored this chemistry would accelerate rather than arrest the decay.

In the end, the Winter Baths emerge as a case study in how Roman builders married imperial engineering knowledge to local geology, balancing logistics against performance with a precision that thermal modeling has only now made legible. By treating mortars not merely as glue but as chronological and technological documents, the research provides both a corrected timeline for the monument’s evolution and a rigorous template for designing compatible restoration materials, one based on the very recipes Roman craftsmen mixed nearly eighteen centuries ago. For a site whose excavated area still covers only a fraction of its ancient footprint, the stones and mortars of Thuburbo Majus are proving to be its most eloquent historians.

Subject of Research: Archaeometric characterization of Roman building stones and mortars from the Winter Baths of Thuburbo Majus, Tunisia

Article Title: Multi-analytical characterization of construction materials from the ‘Winter Baths’ of Thuburbo Majus (Tunisia): Implications for architectural chronology and conservation

Article References: Zaddem, A., Zoghlami, K., Fort, R., Romdhane, H. B., Coralini, A., & Gasmi, M. (2026). Multi-analytical characterization of construction materials from the ‘Winter Baths’ of Thuburbo Majus (Tunisia): Implications for architectural chronology and conservation. Archaeological and Anthropological Sciences, 18(10), Article 205. https://doi.org/10.1007/s12520-026-02563-w

Image Credits: AI Generated

DOI: 10.1007/s12520-026-02563-w

Keywords: Thuburbo Majus, Roman baths, archaeometry, mortars, hydraulic lime, cocciopesto, petrography, X-ray diffraction, Tunisia, conservation, building chronology, gypsum mortar

That question has now been answered with laboratory evidence rather than stylistic argument. In a study published in American Antiquity, researchers at the Florida Museum of Natural History combined chemical fingerprinting with microscopic analysis of pottery from Tampa Bay and concluded that the vessels were made locally by migrants from the Florida Panhandle, the center of gravity of Mississippian culture. These artisans apparently carried specialized knowledge of clay processing and vessel construction hundreds of miles south, then used that expertise to establish a niche for themselves within the region’s existing Safety Harbor communities. The findings resolve a debate that has simmered since the sherds were first shelved in museum collections a century ago.

The cultural backdrop explains why the pottery was so puzzling. Around 1000 A.D., a new way of life took root in the Mississippi River Valley and radiated outward across much of the Midwest and eastern United States. In the heartland, Indigenous communities organized into regional hierarchies, with large chiefdoms concentrating political power over surrounding villages. They planted extensive fields of maize and quarried earth to build flat-topped mounds crowned with temples and elite residences. Tampa Bay, by contrast, sat on the southern edge of this world. The regional culture there, known as Safety Harbor, shared some Mississippian traits: communities aggregated into small chiefdoms, the largest centered on the Tocobaga, with the Mocoso, Pohoy and Uzita chiefdoms nearby, and they too built platform mounds. But no local group amassed the political scale of the northern centers, and the coastal communities never adopted maize agriculture, sustaining themselves instead on fishing and marine resources.

Given these mixed signals, archaeologists never fully understood how closely the coastal chiefdoms were tied to the Mississippian heartland, and the presence of Mississippian-style decorated pottery only deepened the uncertainty. Surface designs alone could not settle the matter, because motifs can be copied. What was needed was a way to look beneath the decoration, into the invisible decisions a potter makes before a vessel is ever fired. Trevor Duke, who began the research as a doctoral student at the University of Florida, and his colleagues assembled a sample of 58 pottery sherds from Tampa Bay, including both plain wares used for everyday cooking and serving and decorated vessels likely reserved for special occasions.

The first test targeted the clay itself. Using neutron activation analysis, the team measured the chemical composition of the sherds and compared it with that of raw clay sources around the region. The profiles matched, showing that every vessel in the sample, decorated or plain, had been made on-site from local clay. That result eliminated the trade hypothesis: the pots had not been manufactured in the Mississippian heartland and carried south. But chemistry could not yet rule out imitation, because a local potter copying northern designs would also use local clay. The decisive evidence had to come from the recipe hidden inside the paste.

To recover it, the researchers turned to petrography, a technique in which a thin slice of a pottery sherd is polished down to roughly half the width of a human hair. Light from a polarizing microscope passes through the section, revealing the voids, cracks and mineral grains that record how the clay was processed. The minerals can be identified by their color and shape under magnification, and from that, researchers can determine what was mixed into the clay. It is, in effect, a fingerprint of the people who made the vessel, preserving choices that no surface decoration can disguise.

Under the microscope, the Tampa Bay pottery revealed its secret. Several of the decorated fragments were tempered with grog, crushed pieces of old pottery mixed into fresh clay, a hallmark of some Mississippian pottery that improves a vessel’s ability to withstand the high temperatures of firing and cooking. Grog tempering appeared in none of the plain samples from Tampa Bay, but in the Tallahassee Hills, home to the nearest massive Mississippian mound center some 200 miles to the north, it is the standard tempering technique for all vessels. The connection ran deeper still: within the grog, the scientists identified mica, a shiny silicate mineral common to the Panhandle but not typically found in peninsular Florida. The host clay was local, but the particles mixed into it had come from the Mississippian heartland, apparently carried south by the potters themselves.

The contrast between the two vessel classes was stark. While 80 percent of the decorated pottery contained grog, not a single plain sherd did; most plain vessels were tempered with chunks of dry clay or sand, methods used in the region for the previous 3,000 years. The decorated pots were also shaped by coiling, the Mississippian technique, rather than molding, and were made with more consistent paste recipes, suggesting potters with advanced knowledge of clay processing. The plain wares, by contrast, were molded, a simple practice that could be quickly learned by novices as the region’s population grew. The most likely reconstruction is that migrant potters traveled from northern Florida carrying bags of their old decorated vessels, then crushed and ground that homeland pottery into the fresh clay of their new home. Every grog-tempered vessel contained multi-generational grog, fragments embedded within larger fragments like Russian nesting dolls, traceable through several generations of pots, and always drawn from the same lineage of decorated vessels. The migrants were quite literally incorporating pieces of their homeland into everything they made.

That expertise appears to have been the migrants’ ticket into an unfamiliar society. Their skill and their connection to Mississippian tradition would have set them apart, transforming commonplace homeland practices into valued services. Yet the knowledge stayed confined. The distinction between decorated and plain pottery persisted for centuries, and local residents never adopted the new techniques, whether because access was restricted or because the skills were simply too tightly held. The tempering, coiling and paste consistency are not clearly visible in a finished pot, so they cannot be easily mimicked without intimate access to the makers. The decorated vessels were also made from higher-quality clays than the plain wares, indicating the migrant artisans were granted access to a limited resource. As one of the researchers noted, secrets of this kind must be broadcast in part, so that people know a secret exists, and the circulating high-quality pots did exactly that, advertising a craft whose inner workings remained out of reach.

The study also offers a broader lesson in how migration reshapes material culture. Specialized knowledge passes directly from mentor to learner, and by tying homeland pottery into a chain of crushed and reused fragments across generations, the migrant potters may have been carrying their ancestors’ vessels into each new pot and the next generation. In Tampa Bay, a community of artisans found a way to matter in a new place, and the evidence of their arrival was hiding in plain sight for a century, waiting for the right instruments to read it.

Subject of Research: Compositional analysis of Mississippian-style pottery revealing migrant potters in pre-Columbian Tampa Bay, Florida

Article Title: Archaeologists uncover centuries-old mystery of Tampa Bay’s secret community of migrant potters

Article References: Archaeologists uncover centuries-old mystery of Tampa Bay’s secret community of migrant potters. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: Mississippian culture, Tampa Bay, Safety Harbor, pottery analysis, neutron activation analysis, petrography, grog tempering, migration, Florida archaeology, American Antiquity, Tocobaga, Florida Museum of Natural History

Utrecht occupies a special place in medieval Dutch ceramic history. The earliest evidence for pottery production there dates to the late 12th century CE, and by the 14th century the town had joined Haarlem, Leiden and Breda as a major manufacturing centre supplying both local markets and wider regional trade. Its products have been recovered as far afield as Alkmaar, Haarlem, Dordrecht and Amsterdam. The workshops themselves clustered in the suburbs of Bemuurde Weerd and Tolsteeg, north and south of the town walls, and along the banks of the Vecht river, where excavations have uncovered nine vertical updraft kilns with brick or clay floors, round or oval in plan and measuring up to five metres long.

The excavated waste heaps tell a story of technological transition. The first production phase at Zeedijk, dated 1150 to 1175 CE, yielded almost exclusively grey, round-based jars. After an apparent hiatus of roughly a century, the second phase, from 1275 to 1350 CE, saw a wider repertoire including lead-glazed reddish tripod forms, jugs, bowls and pans, though grey jars remained dominant. By the third phase, represented by the Oosterkade workshop (1350 to 1400 CE) and riverside workshops such as Anthoniedijk, Hogelanden and Lauwerecht (1375 to 1425 CE), lead-glazed redware had become far more prominent, and unglazed and lead-glazed floor tiles were also being produced.

To characterise the raw materials and firing technology, the team subjected the 59 samples, plus one clay sample from a waste pit at Bemuurde Weerd, to a battery of techniques: polarised light optical microscopy, wavelength-dispersive X-ray fluorescence spectrometry, X-ray diffraction and scanning electron microscopy with energy dispersive X-ray spectrometry. Thin-section petrography revealed two main fabric groups, a Coarse Group with large, moderately to poorly sorted quartz inclusions and a Fine Group with smaller, better-sorted inclusions. The size, rounded shape and bimodal distribution of the coarse quartz grains suggest they were deliberately added as temper, most likely derived from fluvial deposits, consistent with the Holocene river clays of the region.

The chemical data, measured on 26 major, minor and trace elements at the Fitch Laboratory of the British School at Athens, showed a strongly homogeneous, silico-aluminous dataset pointing to local clay sources. Principal component analysis identified three compositional groups, with a large, homogeneous group A accounting for more than 70 percent of the samples. All the Utrecht products were made from calcium-poor, iron-rich clay, with calcium contents below 2.5 percent, and the chemical similarity between the fired clay sample and the pottery, despite differences in calcium, may itself be evidence of quartz tempering. X-ray diffraction confirmed the mineral assemblage of quartz, illite-muscovite, K-feldspar and plagioclase, with redware bodies generally containing more hematite than greyware.

Firing temperatures emerged as consistently low. Most of the ceramics, 44 of them, were fired below 800 degrees Celsius, while a handful containing the high-temperature minerals gehlenite, diopside and mullite may have reached roughly 850 to 900 degrees or slightly above. The co-occurrence of surviving calcite and dolomite with these high-temperature phases implies short soaking times in the kiln. The glazes told their own story: single-layered, transparent coatings up to about 250 micrometres thick, of very high to high-lead type, with lead oxide contents between roughly 51 and 69 weight percent. Comparisons of corrected glaze and body compositions indicate that potters mixed lead oxide with silica before application, and that the yellowish-brown to greenish colour came from iron in the glaze over the reddish ceramic body.

The most novel element of the study was the application of small-angle neutron scattering, or SANS, to the question of how the vessels were formed. Measured non-destructively at the YS-SANS instrument of the Budapest Neutron Centre, 38 jar samples yielded data on the orientation and alignment of nanoscale domains in the ceramic fabric, which record the forces applied during forming. Thirty-two samples showed high isotropy values, indicating disorganised internal structures characteristic of percussion-building techniques such as pinching, moulding or tamper-and-concave-anvil forming. Combined with the wheel-made traces on rims and necks, this points to a two-stage strategy the authors call percussion-wheeling: the body formed by percussion, then the neck and rim refined on a rotational device.

Only six samples showed the low isotropy and significant tilting angles diagnostic of other techniques. One redware jar from the second phase at Zeedijk proved to be coil-built and wheel-shaped, while five jars, from both Zeedijk and Oudenoord, were genuinely wheel-thrown, three with clockwise and two with anticlockwise wheel rotation. Notably, all the wheel-thrown examples date to the second production phase after about 1275 CE, confirming a previously observed typo-technological shift from grey hand-formed jars to reddish tripod forms. Contrary to common expectations, the potters did not favour fine fabrics for wheel-throwing; nearly all the wheel-thrown jars were made from the coarse fabric. The persistence of percussion-wheeling across the 100-year hiatus between the first and second phases suggests a conservative, culturally embedded technological tradition, one perhaps also suited to producing the round-based jar shapes that were difficult to throw on a wheel.

The study also cautions against reading forming techniques from surface features alone. Interior depressions often interpreted as fingertip impressions from moulding appeared on wheel-thrown vessels too, and may instead reflect hands supporting the vessel wall during brushing, while interior ridges below the neck, sometimes taken as evidence of added coils, also occurred on wheel-thrown jars and may result from clay displacement during wheel work. The reasons for discarding the wasters were largely firing failures: warping and cracking from overfiring, loosened tripod legs and handles, and glazes accidentally fired in a reducing atmosphere. Taken together, the results portray a production tradition defined by both continuity and change, in which local potters favoured iron-rich, calcium-poor clay, tempered it with river sand, fired at low temperatures, and gradually adopted wheel-throwing and lead glazing, offering archaeologists a new quantitative template for reconstructing medieval craft knowledge and its transmission.

Subject of Research: The production technology and chaîne opératoire of medieval greyware and redware ceramics from 12th to 15th century Utrecht, the Netherlands

Article Title: Advancing the chaîne opératoire analysis of medieval greyware and redware ceramics: A case study from 12th to 15th centuries CE Utrecht, the Netherlands

Article References: Borgers, B., Gait, J., Bajnok, K., Allepuz, E. T., Bajnóczi, B., Len, A., & Griffioen, A. (2026). Advancing the chaîne opératoire analysis of medieval greyware and redware ceramics: A case study from 12th to 15th centuries CE Utrecht, the Netherlands. Archaeological and Anthropological Sciences, 18(9), Article 194. https://doi.org/10.1007/s12520-026-02554-x

Image Credits: AI Generated

DOI: 10.1007/s12520-026-02554-x

Keywords: medieval pottery, Utrecht, chaîne opératoire, ceramic technology, greyware, redware, small-angle neutron scattering, lead glazes, petrography, X-ray fluorescence, pottery workshops, the Netherlands