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Article

Archaeological Stratification in the St. Leucio Basilica (2nd Century BCE–6th Century CE, Canosa di Puglia, Southern Italy): Archaeometric Analysis of Pebble Pavements

by
Giovanna Fioretti
1,*,
Alessandro D’Alessio
2 and
Giacomo Eramo
1
1
Earth and Geoenvironmental Sciences Department, University of Bari Aldo Moro, 70121 Bari, Italy
2
Archaeological Park of Ostia Antica, Ministry of Culture, 00135 Rome, Italy
*
Author to whom correspondence should be addressed.
Heritage 2025, 8(6), 186; https://doi.org/10.3390/heritage8060186
Submission received: 9 April 2025 / Revised: 17 May 2025 / Accepted: 19 May 2025 / Published: 24 May 2025
(This article belongs to the Special Issue Multianalytical Approaches Applied to Conservation and Restoration Strategies in Cultural Heritage)
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Abstract

:
This paper presents the results of an archaeometric investigation of the preparatory mortars of the pebble pavements of the Basilica of St. Leucio in Canosa di Puglia (Bari, Southern Italy). The main aim of the presented study is to contribute to the dating of some portions of the pebble pavements by analyzing the preparatory layers and determining whether they pertain to the basilica (6th century CE) or to the pre-existing temple (2nd century BCE–4th century CE). Further purposes are to provide information about the production technologies of the mortars and to identify the nature of the pigments found on some pebbles. In order to contribute to the dating studies of the floors, complicated by previous reuse and restoration, 12 samples of mortars, sometimes including pebbles, were collected in different areas of the site. They were analyzed by polarized light microscopy (PLM), X-ray diffractometry (XRPD), X-ray fluorescence spectroscopy (XRF), and scanning electron microscopy coupled with an energy-dispersive spectrometer (SEM-EDS). The results allowed us to advance chronological data on different pavement areas, to deepen our knowledge on mortar production, in terms of both raw materials and technology, and to identify red ochre as the pigment with which the pavement surface was painted.

1. Introduction

Archaeometric analyses of bedding mortars play a crucial role in the study of ancient mosaics or pavements with tesserae, as they combine petrographic, mineralogical, and chemical data with deep technological aspects to identify the provenance of raw materials, to assess essential findings for dating of archaeological sites, and for understanding their restoration history. Recent archaeometric studies, often based on a multi- and interdisciplinary approach, have contributed significantly to our knowledge of the provenance, production techniques, and material composition of ancient floors.
For instance, significant archaeometric investigations were carried out on the mortars of the glass mosaic from the Villa del Casale in Piazza Armerina, Italy [1], providing valuable insights into the raw materials and manufacturing techniques employed at this highly important archaeological site. Similarly, Izzo et al. [2] applied a mineralogical and petrographic approach to examine the production technology of mortars used in the mosaic floors of ancient Stabiae (Naples, Italy). Calia et al. [3] focused on the mortars of the mosaic in the crypt of St. Nicholas in Bari (Italy), aiming not only to identify the raw materials but also to assess the degradation products. An interesting archaeometric characterization was carried out on the bedding mortars of the Domus delle Bestie Ferite and the Domus di Tito Macro sites in Aquileia (Italy), highlighting the evolution of mortar preparation techniques over time and their relationship with the traditional Roman formulations [4].
Moreover, the integration of analytical results with digital representation techniques has further enhanced research outcomes, as demonstrated in the archaeometric study of floor mosaic mortar substrates from Ancient Messene, in the southern Peloponnese, Greece [5].
Studies comparable to the present case include the archaeometric analysis of mortars and tesserae from other mosaic areas within the site of St. Leucio in Canosa [6], as well as investigations conducted at other significant archaeological sites of the city, such as the Christian Episcopal complex of St. Pietro [7] and the baptistery of St. Giovanni [8,9].
Focusing on the archaeological site of St. Leucio in Canosa di Puglia, it is characterized by the presence of two distinct flooring systems: one belonging to the basilica (6th century CE) and another, chronologically distinct, associated with the Italic temple (2nd century BCE–4th century CE) upon which the basilica was built [10,11,12]. For each of them, some types of mosaic, different in lithology, color, shape, and size of pebbles and decorative motif, are put together. The dating of floors is very difficult; on the one hand, due to the reuse of spolia [13], consisting in the relocation of capitals, semi-columns, and flooring fragments; and on the other hand, due to early restoration programs carried out in the 1970s, which were conducted without documentation, resulting in a chronological mixing of materials and construction techniques.
The main aim of the presented study is to contribute to the dating of some portions of the pavements (part of which has already been dated) by analyzing the preparatory layers and determining whether they pertain to the basilica or to the Italic temple. Furthermore, further purposes are to provide information about the production technologies of the mortars and to identify the nature of the pigments found on some pebbles.

The Site of the Italic Temple and the St. Leucio Basilica

Built at the beginning of the 2nd century BCE, the temple of Minerva in St. Leucio (Canosa di Puglia) was used until the middle or more probably late imperial age (4th century CE), when it was effectively abandoned. It was a large rectangular building (about 39 × 29 m) oriented N/NW towards the town and the acropolis of Canosa, on the front and back of which towered two imposing colonnades of at least ten Ionic columns, surmounted by an entablature comprising a Doric frieze with triglyphs and figured metopes and an Ionic cornice with leonine proteome drip moldings (Figure 1a). Nearby and parallel to the front and rear sides, two internal foundation structures supported presumably continuous walls, in the middle of which were two axial entrances, the one on the north (main) side probably wider than the other on the south side. The temple flanks were also probably continuous walls, perhaps with Ionic half-columns on the outside, but it cannot be ruled out that they also had openings interspersed with two or three columns with Ionic or Corinthian figured capitals. If the latter were half-capitals, as they appear today, it is possible instead that they were part of half-columns leaning against the inside of the large quadrilateral, in the center of which stood a cella/oikos (7.50 × 9.60 m inside) intended to house the cult simulacrum and perhaps slightly elevated above the temple floor, a beautiful cement floor with cut polychrome pebbles and a rubricated surface. Lastly, as far as roofing is concerned, while the cella/oikos presumably had roofing and the spaces between the colonnades and the elevated walls behind were topped by trusses and pitched roofs, the inner quadrilateral was probably uncovered, as the same workmanship and finish of the flooring would suggest [14,15].
During the 6th century, the great basilica built by Sabinus, bishop of Canosa from 514 to 566, initially dedicated to Saints Cosmas and Damian and only later re-titled to St. Leucio, was erected over the remains of the abandoned temple. The floor plan of the basilica (Figure 1b,c) is very particular, consisting of a double tetraconcus, i.e., a large external square (47 × 47 m) with continuous masonry blocks at the bottom and batten masonry at the top, with four apses in the center of each side (28 m), consisting of pillars made of blockwork with masonry reinforcements in L-shaped masonry at the corners and rectangular at the heads of the four apses that also articulate it on each side, with these being delineated by a circle of four columns instead of solid masonry as in the larger square. The two squares thus delimit a four-armed ambulatory, communicating through the passages between the pillars with a large central space [10,16,17]. It is therefore an absolutely peculiar planimetric layout, which has been proposed to date back to Syrian models (great basilica of Antioch, four-cornered churches of Apamea, Seleucia of Pieria, Aleppo, Emesa, Bosra, Resafa), but also attested in the Balkans (Ocrid, Adrianople, Philippopolis), in Athens (Basilica of Eudocia), in Egypt, and later in Armenia [11,12,18,19], while in Italy the only similar example is the St. Lorenzo Maggiore in Milan.
Within the archaeological site, in addition to the conspicuous remains of the wall structures pertaining to the two cult buildings, large portions of the flooring of both the pagan temple (in river pebbles) and the church (remakes and/or additions to the latter, and especially the splendid polychrome mosaics that occupy the ambulatory arms and the south, east, and west apses of the basilica) are preserved. In this contribution, we will focus in particular on the first set of evidence, namely, the pebbles pavement (or pavements), quickly illustrated below.
Alternatively attributed to the Hellenistic–Italic temple and to the Christian basilica [20], the cobblestone pavement of St. Leucio actually reveals far more complex framing problems than hitherto thought. Today, it is known in fact that the paving of the older building (still partially preserved inside) was reused and integrated in some portions, also made of pebbles and other stone elements, at the time the church was built, if not during later interventions [14,21,22,23]. The restoration work of the floors, as well as the mosaic carpets in the basilica, were carried out in the 1960s, and especially those conducted in 1978–1979 certainly played a part in the difficulties of correct attribution. In fact, especially on the latter occasion, the work was very demanding and involved the removal and subsequent relocation of large sections of the floor, often with the use of the same pebbles.
For these reasons, the ‘Sapienza’ University of Rome conducted a systematic mapping of all existing floor surfaces in the years 2005–2007, which allowed for a reconstruction with a good degree of approximation of the succession of events that happened to the cobblestone pavement from the time of its first laying in the Hellenistic period to the early Christian and early medieval periods [20]. Based on the data from the study, it is clear that large portions of the original floor are still preserved in situ in at least three sectors within the monument: one in the area roughly corresponding to the portion immediately to the west of the central cella/oikos of the Hellenistic temple; a second involving a narrow but prolonged strip to the east of the same cella/oikos; and lastly, a third at the eastern end of the space between the northern decastyle front of the temple and the wall behind it, delimiting the inner and hypetral space, in the center of which the cella/oikos stood. Other conspicuous remains seem to be discernible in the remaining northern portion and further along in the south-eastern sector of the hypetral space, but modern restoration work carried out there has complicated the understanding of the original arrangement.
As concerns the cobblestone floor of the temple, which was, as mentioned, partially maintained in use inside the basilica, very different features can be seen in the portions that can be traced back to the construction of the church: in particular, there is a large section located at the north ambulatory arm, immediately east of the apse, where the dismantling of the columns and the underlying temple bases determined the need to fill in the space by integrating the flooring itself. That we are not dealing with a modern restoration is assured by comparing the currently visible situation with some photographs from August 1964, which can be traced back to the anastylosis work following the excavations that brought the entire complex to light; from which images it is clear that the paving placed to fill the hollow housing the bases, found there and attributable precisely to the time of the basilica’s construction, was then partially dismantled in order to mark the position and dimensions of the bases themselves on the ground (moreover, with doubtful scanning of the intercolumnia). It should also be emphasized that this and other floor pieces belonging to the church differ markedly from those of the pre-existing temple in terms of quality, size, and laying of the lithotypes used, which were not only of fluvial origin and gray and brown in color, but also derived from the crushing of blocks and/or slabs of micritic limestone, white and colored marble, etc., all measuring between 2 and 4 × 4 or 8–12 cm, placed mostly in bands and with the long sides placed side by side.
Finally, it should be noted that the analysis conducted revealed the presence of large portions paved with cobblestones, whose shape and arrangement (generally small and whole) leave one wondering whether this could be a third type, perhaps attributable to one or more reconstructions carried out during the long life of the temple, which, as mentioned, certainly still existed in the late imperial period.

2. Sampling and Material

The analyzed group consisted of 12 samples, which were essentially composed of preparatory mortar, sometimes including a pebble. The sampling was carried out while preserving the conservation state of the pebble pavement [24,25]. In some cases, mortars showed traces of red painting. The sampling points are marked on the site map in Figure 2 and some of these are displayed in Figure 3. The selection involved 4 types of pavements: (i) an undated part characterized by brown, yellow, white, and gray cut pebbles with a medium length of 6 cm (type 1, Figure 3a); (ii) an undated portion showing angular white and gray marble pebbles, mainly squared, with a mean length of about 5 cm (type 2, Figure 3b); (iii) a portion of pebble pavement belonging to the temple floor consisting of white, yellow, green, brown, and gray cut pebbles (about 6 cm) and traces of red color on the joint mortar (type 3, Figure 3c); (iv) a part of the basilica floor, with very elongated gray and brown cut pebbles having a length of about 6 cm (type 4, Figure 3d).
The mortar group was composed of not layered or layered mortars. A short description, the type of pebble pavement (where visible), the building phase, and the analytical methods applied to each sample are reported in Table 1, and more details on features of the mortars are summarized in Table S1 (Supplementary Material).

3. Methods

The first step of the archaeometric investigation involved a macroscopic study of the samples, which were previously photographed and labeled.
For all the samples (both mortars and pebbles), a stratigraphic analysis and a petrographic characterization of mortars in thin-section were performed using an Axioskop 40 POL (Zeiss, Oberkochen, Germany) polarizing optical microscope. Images were acquired with a DS-Fi1c CCD camera (Nikon, Tokyo, Japan) with an associated Nikon Digital Sight DS-U2 controller unit. The aggregate and void abundances were provided by visual estimation using comparison charts [26].
The XRPD and XRF investigations were carried out on 7 not-layered mortars. Layered mortars (5 samples) were excluded from these investigations.
For the mineralogical analysis by X-ray powder diffraction (XRPD), a PANalytical X’Pert pro MDS powder diffractometer (Malvern, PANalytical, Almelo, The Netherlands), with a PANalytical X’Celerator detector (Malvern, PANalytical, Almelo, The Netherlands), was used. The X-ray tube (Cukα) was operated at 40 kV and 40 mA. All XRPD spectra were processed with the X-Pert Highscore software (PANalytical, version 3.0), with a PDF-2 reference database (ICDD) for identification of inorganic phases. The diffraction peaks of the XRPD spectra were compared to a JCPDS-ICDD diffraction chart and the crystalline phases thereby identified.
The bulk chemical analysis of the potsherds and local clays was performed by an automatic spectrometer PANalytical AXIOS-Advanced, equipped with an X-ray tube X SST-mAX (Rh anode). The major oxides and trace element concentrations were determined after the analytical techniques outlined by Franzini et al. [27,28] and Leoni and Saitta [29]. The detection limit for major element oxides was 0.01 wt. % and for trace elements about 10 ppm. The accuracy was checked using two international standards (AGV-1 of USGS-USA and NIM-G of NIM-South Africa). Loss on ignition (LOI) was determined by heating the samples at 1000 °C for 12 h.
Morphological observation and an elemental analysis of aggregates, binder, and painted layers were obtained on two representative samples including the three mortar types, red painting, and cocciopesto fragments by means of a scanning electron microscope (SEM-EDS). The observation was made on thin-sections fixed on an aluminum specimen holders and metallized with graphite. The instrument was a SEMEVO-50XVP (LEO) (Zeiss, Oberkochen, Germany), equipped with an AZTEC (Oxford Instruments, Abingdon, UK) EDS microanalysis system with an SD X-MaxN detector (80 mm2). The measurement conditions were as follows: 15 kV accelerating potential, 250–500 pA probe current, and 8.5 mm working distance.
The accuracy of the analytical data was verified using various standards produced by Micro-Analysis Consultants Ltd. (St. Ives, UK). Spectra acquisitions lasted 50 s, with counts ranging from 25,000 to 30,000. Chemical maps were acquired with a dwell time of 100 μs, a counting time of 10 min, and a resolution of 2048. The correction of the X-ray intensity was performed following Pouchou and Pichoir [30] Analytical precision (σ) was 0.5% for concentrations > 15 wt.%, 1% for concentrations of approximately 5 wt.%, and up to approximately 30% for concentrations near the detection limit. Different Micro-Analysis Consultants Ltd. (UK) mineral standards were used to check the accuracy of the analytical data.

4. Results

4.1. Petrography

A preliminary macroscopic observation, further refined under an optical microscope, revealed the presence of stratigraphy in some samples (MSL03, MSLC03, MSL11, MSL12). In these cases, each layer was considered as an individual element. Conversely, the remaining samples were composed of a single homogeneous mortar (Table 1).
Based on petrographic characteristics, mineralogical composition, texture, and porosity, three petrographic groups were identified (Figure 4, Table 2). A table summarizing detailed petrographic data for each mortar is reported in the Supplementary Material (Table S1).

4.2. CP Group

Generally, the CP-type mortars showed a carbonate binder with a micritic texture, marked by a heterogeneous structure increased by different carbonatation degree areas and for the presence of underburnt relicts, large lime lumps, angular and complex pores.
The distinctive feature of this group was the significant presence of cocciopesto as aggregate, together with a smaller amount of monocrystalline and polycrystalline quartz fragments, pyroxenes, numerous lime lumps, some underburnt relicts, lithic fragments, some fossils, and iron oxides (Figure 4a). The abundance of the aggregate varied between 20 and 40% vol.
It is important to note that the cocciopesto fragments, despite their varied color shades, could be classified into two distinct types. Cocciopesto A was brown and exhibited a calcareous silt matrix with inclusions of quartz, pyroxenes, muscovite, and a significant amount of iron oxides. Cocciopesto B had a greenish hue and was characterized by a quartz–silt matrix containing inclusions of pyroxenes, muscovite, ferruginous aggregates, and felspars. The samples belonging to this group were MSL01, MSL02, MSL04, MSL07, MSL12, MSL03 (layer A), MSL11 (layer B), and MSLC3 (layer B).

4.3. MIC Group

Mortars in this group (Figure 4b) showed a carbonate binder with a micritic texture and a rather homogeneous structure. The porosity value was very low (<5%) and pores were generally rounded. The aggregate, ranging between 40 and 50% vol., was predominantly composed of micritic carbonate fragments, with a secondary contribution from monocrystalline quartz, lithic fragments, fossils and iron oxides. Within this group, a further distinction involved mortars characterized by aggregates exclusively consisting of carbonate rock fragments (MIC1, sample MSL05) and mortars rich in bioclasts in addition to carbonate rock fragments (MIC2, samples MSL06 and MSL10).

4.4. MST Group

This mortar type (Figure 4c) was defined by a carbonate binder with micritic texture and heterogeneous structure. Some lime lumps were scattered. The aggregate consisted of a natural sand (30–40% vol) including numerous lithic, carbonate, and chert fragments, and several minerals, among which were monocrystalline and polycrystalline quartz, feldspars, amphiboles, and pyroxenes. The porosity was almost zero and the rare voids showed both angular and rounded shape. Samples belonging to this group included MSL03 (layer B), MSL11 (layer A), and MSLC3 (layer A). The porosity was very limited.

4.5. Mineralogy

A semiquantitative XRPD analysis was carried out on seven samples of homogeneous mortars. Table 3 reports a summary of the diffractometry results and in Figure 5 the XRPD spectra of representative samples of MIC-type (Figure 5a) and CP-type (Figure 5b) mortars are shown. As explained in the Sampling and Material and Methods sections, XRPD was carried out only for not-layered samples; the reason being that MST-type samples, always found in layered samples, cannot be studied in this sense. The most abundant mineral was calcite, followed by quartz. The presence of quartz is significant in samples including cocciopesto (CP group: MSL01, MSL02, MSL07, and MSL12), whereas it is negligible in mortars with natural aggregate (MIC group: MLS05, MLS06, MSL10). Variable amounts of feldspar were recognized in all the samples, except for MSL06. Traces of clay minerals (illite–muscovite) characterized all the investigated mortars. Traces of diopside were found in the MSL02 and MSL12 spectra and traces of gehlenite were recorded in samples MSL01 and MSL12.

4.6. Chemical Composition

The XRF investigation results (Table 4), carried out on seven not-layered mortars, revealed that the predominant oxide was CaO, which varied between 33.9 and 53.7% wt. The next most significant contribution was from SiO2, which ranged between 1.8 and 25.3% wt. Specifically, in samples with cocciopesto as aggregate (CP group: MSL01, MSL02, MSL07, MSL12) the CaO–SiO2 ratio decreased as displayed in the plot in Figure 6, where a high homogeneity in their relationship is observable as well. In contrast, in samples without cocciopesto and with natural aggregate (MIC group: MLS05, MLS06, MSL10), the CaO–SiO2 ratio, although heterogeneous, seemed to be higher.
The trend of Al2O3 followed the same tendency, as it ranged from 3.15 to 6.4% wt. and from 0.6 and 3.18% wt. in mortars with and without cocciopesto, respectively.
Other minor oxides (>1% wt.) included, in order of overall abundance, Fe2O3, MgO, K2O, Na2O, TiO2. Traces of P2O5 and MnO were also attested.
Additional data were obtained by a SEM-EDS analysis. For this investigation, two polished thin-sections were selected: MSL10, representative of the MIC-type mortar; and MSL12, representative of the CP- and MST-type mortars, as well as the red paint layer on the surface of the pebble pavement. All results obtained from the EDS analysis are reported in Table S2 in the Supplementary Material, while an extract showing the main elemental compositions of the three mortar types is provided in Table 5.
EDS measurements were carried out on 11 areas of the binder in sample MSL10, and elemental mapping of the area was also performed (Figure 7a). As shown in the map, the binder used in the MIC mortar was air lime-based; however, the sum spectrum presented in Figure 7b reveals significant contributions from Si and Al, followed by Mg, K, and Na, which can be attributed to the fine fraction of the aggregate intimately blended with lime.
In sample MSL12, three distinct areas were examined, each with a specific purpose.
Area B, for which the elemental map is reported in Figure 7c, included both CP- and MST-type mortars. A total of 10 EDS acquisitions were performed: 7 for the CP-type mortar (B1–B7) and 3 for the MST-type mortar (B8–B10). A representative spectrum of the CP mortar binder (Figure 7d) showed a predominance of Ca, with lower amounts of Si, Al, Mg, Na, and K, indicating a lime-rich binder and the presence of silicate phases associated with clay minerals. In contrast, the representative spectrum of the MST-type mortar (Figure 7e) displayed a higher contribution of Si, Al, Mg, Na, and K, suggesting a greater presence of clay phases.
Area C of the same sample included fragments of cocciopesto, with an elemental map shown in Figure 8a. Eight EDS measurements were performed in this area, and a representative spectrum of the cocciopesto composition indicates a ceramic with a carbonate-rich matrix (Figure 8b). The line scan across the boundary between the cocciopesto and the binder (Figure 8c) showed a reaction rim of about 30 µm.
Finally, area A of sample MSL12 (Figure 9a) included the layer containing traces of red pigment. In this area, 13 measurements were taken, and 2 representative spectra are presented in Figure 9b,c. These spectra highlight the presence of Fe, suggesting the use of red ochre as a pigment mixed with lime in the paint among the pebbles of the pavement.

5. Discussion

Chemical and mineralogical analyses allowed the identification of the mortar composition. The results suggested that the mortars had a high calcium content, indicating the carbonate nature of the binder used in their preparation [31,32], as proved in the Apulian tradition [33,34,35].
The comparison between these results and optical microscopy highlighted the presence of very homogeneous mortar groups, and their peculiarities made it possible to reveal significant technological aspects [36,37,38].
The CP group consisted of mortars containing cocciopesto, which exhibited high granulometric variability, suggesting a lack of selection and sieving of the aggregate [35,36,37,38,39]. Furthermore, a high density of lime lumps [40,41] and underburnt relicts was observed. The presence of pores with complex and angular shapes also indicated the low fluidity of the mixture [38,39]. These features seemed to be indicative of a sand slaking [42,43]. However, the presence in the binder of clay minerals detected through SEM-EDS on the one hand, and of cocciopesto on the other hand, suggested an intentional addition to provide hydraulic properties to the mortars [44,45,46,47,48,49,50,51,52,53,54]. An XRPD analysis revealed also the presence of diopside and gehlenite, which are products of high-temperature firing of Ca-rich clays, and their presence in the mortar is clearly connected to the cocciopesto aggregate [55].
Therefore, the defects in mortar production cannot be attributed so much to a lack of technological knowledge as to the specific bedding function that this mortar fulfilled.
The MST-group samples showed the presence of a natural sandy aggregate with sub-rounded shape, composed of pyroxene, chert, and polycrystalline quartz fragments with strongly undulous extinction (Figure 10a,b), suggesting a fluvial origin of the raw materials used as aggregate [56].
The petrographic MIC-group samples were characterized almost exclusively by rounded porosity and lime lumps. For this reason, it was evident that these mortars (as well as those of the MST group described above) were prepared with much greater care, resulting in a significantly more fluid mixture [38,39], setting them apart from the CP-group mortars.
Briefly focusing on the pebbles, a distinctive characteristic was identified in the samples containing marble pebbles, particularly in MSLC09 (Figure 10c) and MSLC03 (Figure 10d). A petrographic analysis revealed that these marbles exhibited different degrees of metamorphism of the original limestones. This distinction could correspond to sourcing from different quarries. However, from the absence of outcropping marble deposits in the surrounding areas, it appeared plausible that both marble pebbles were the result of the reuse of pebbles of spolia of the temple structure [13].
The classification of samples based on the petrographic analysis and their grouping into the three mortar typologies provided new insights for dating purposes [57,58,59].
In particular, the CP group included mortars of uncertain dating (MSL07 of 1-type pavement and MSL12) and mortars belonging to areas previously attributed to the temple (MSL01 and MSL02, both belonging to 4-type pavement, and MSL03, MSLC03, and MSL04, all belonging to 3-type pavement).
Among these latter samples, sample MSL04, which was a reused block within the basilica walls [13], is significant, certainly belonging to the earliest period of building; the very high homogeneity of the samples of this group, also proved by the XRF results (Figure 6), confirmed the correspondence of the CP group with the temple construction phase, allowing us to extend the dating also to samples MSL07 and MSL12. Such a conclusion indicates that 1-type, 3-type, and 4-type pavements were created using the same mortar and in the same period (temple floor).
Moreover, the MIC group contained a sample (MSL05, 4-type pavement) of the Christian basilica floor and two samples (MSL06 from 1-type pavement and MSL10) whose dating was undetermined. Also in this case, the petrographic features of samples of the MIC group and their similarity suggested that all samples of the MIC group showed the same mortar and belonged to the same construction period.
However, attributing these areas to the construction of the basilica would be incorrect, as the 1-type and 4-type pavements are, as previously demonstrated, associated with the temple flooring. The presence of pavements in the basilica area with mortar different from that used for the temple (CP group) but the presence of the same types of pavement (1- and 4-types) suggested only one hypothesis: the pebble pavement hosted in the basilica floor must result from the exclusive reuse of pebbles of the temple pavement, set in a new mortar (MIC) during the construction of the basilica.
A crucial indicator providing further data for relative dating of mortars, and consequently for establishing a chronological correlation between the different pavement areas analyzed in this study, was the presence of stratified mortar samples. For this purpose, the relationships between mortar types within the same sample and their contact surfaces were considered.
For instance, MSL03 (Figure 11a) was a stratified sample consisting of a CP-type mortar over which an MTS-type mortar was applied. The boundary between the two mortar layers was very clear. This suggested that the upper mortar (MST-type) was applied when the underlying mortar had already completely dried, likely during a restoration phase. In addition, in sample MSL11 (Figure 11b) the upper mortar belonging to the MST group was clearly a repair mortar, indicating that it was applied well after the underlying mortar layer (CP-type). Further confirmation came from sample MSLC03, where the contact surface between the CP-type and MST-type mortars (Figure 11c) was strongly visible.
By extending this observation to all samples within the MST petrographic group, it can be stated that these mortars were significantly later than those in the CP group, probably a restoration addition.
Referring to the painting on the pebble floor, the preliminary macroscopic analysis revealed the presence of a red color on samples MSL02 (4-type pavement), MSL03, MSL04, and MSL11 (all 3-type pavement). Microanalyses using EDS-SEM were conducted to determine the nature of the color and confirmed the presence of iron oxides and then of red ochre [60,61,62]. Red ochre, mixed with lime, was used to paint the mortar joints that emerged among the pebbles. Furthermore, in sample MSL03, the red layer was applied over the MST mortar layer, and the interface between the painting layer and MST mortar layer was gradual (Figure 11d). This indicates that the painting of the pebble pavement was not original or coeval to the creation of the temple floors but rather coincided with the application of the MST-type mortar and therefore with a later restoration phase.

6. Conclusions

An archaeometric approach and the correlation between petrographic, mineralogical, and chemical analyses provided valuable insights into the technological aspects and chronological framework of the pebble pavement of the St. Leucio archaeological site. The clear distinction between CP-, MST-, and MIC-type mortars, as well as their stratigraphic relationships, suggested a sequence of construction and restoration phases. The CP-group mortars, characterized by their heterogeneous composition and technological features, were associated with the temple’s original construction, reinforcing the hypothesis that 1-type, 3-type, and 4-type pavements were laid during the same period. Conversely, the MIC-group mortars, although used for 1- and 4-type pavements, were linked to the basilica phase, confirming the reuse of pebbles from the temple’s pebble floor. The MST-group mortars, identified in stratified samples and featuring clear contact surfaces, were associated with later restoration activities. The application of red ochre paint over MST mortars further corroborates this sequence, indicating that the painted decoration was not original but rather a later intervention. These findings contribute to a more comprehensive understanding of the construction and reuse practices at the investigated site, underscoring the complexity of architectural transformations over time.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/heritage8060186/s1, Table S1: Petrographic features of mortars. Abbreviation: Str = structure; l = layered; nl = not layered; carb = carbonatic; Txt = texture; mic = micritic; ht = heterogeneous; hm = homogeneous; UBR = underburnt relict; LL = lime lump; unim = unimodal; bim = bimodal; mD = modal diameter; maxD = maximum diameter; mQt = monocrystalline quartz; pQt = polycrystalline quartz; Ch = chert; Kfs = K felspar; Mca = micas; Px = pyroxene; LF = lithic fragment; CP = cocciopesto; Fe = iron oxides; Fs = fossils; Table S2: EDS analyses acquired for each raster for the two considered samples. Percentages are normalized to 100.

Author Contributions

Conceptualization, G.F. and G.E.; methodology, G.F. and G.E.; investigation, G.F. and G.E.; data curation, G.F.; writing—original draft preparation, G.F. and A.D.; writing—review and editing, G.F. and G.E.; visualization, G.F. and A.D. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

The original contributions presented in this study are included in the article/Supplementary Materials. Further inquiries can be directed to the corresponding author(s).

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. New reconstructive hypothesis of the temple plan at the level of the foundations and the bases of the columns ((a), elaboration by A. d’Alessio); reconstructive plan of phase I of the basilica ((b), elaboration by A. d’Alessio and E. Gallocchio); reconstructive plan of phase II ((c), elaboration by A. D’Alessio).
Figure 1. New reconstructive hypothesis of the temple plan at the level of the foundations and the bases of the columns ((a), elaboration by A. d’Alessio); reconstructive plan of phase I of the basilica ((b), elaboration by A. d’Alessio and E. Gallocchio); reconstructive plan of phase II ((c), elaboration by A. D’Alessio).
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Figure 2. Planimetry of the St. Leucio site (A. D’Alessio), marked with sampling points.
Figure 2. Planimetry of the St. Leucio site (A. D’Alessio), marked with sampling points.
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Figure 3. Types of pebble pavement: type 1 (a), type 2 (b), type 3 (c), type 4 (d); original position of samples MSL07 (a), MSL09 (b), MSL11 (c), MSL02 (d), and MSL04 (e); detail of the surface of sample MSL04 (f) (A. D’Alessio).
Figure 3. Types of pebble pavement: type 1 (a), type 2 (b), type 3 (c), type 4 (d); original position of samples MSL07 (a), MSL09 (b), MSL11 (c), MSL02 (d), and MSL04 (e); detail of the surface of sample MSL04 (f) (A. D’Alessio).
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Figure 4. Representative microphotos of the three petrographic groups. CP-type (a), showing fragments of cocciopesto A (cpA) and cocciopesto B (cpB), a large lime lump (LL) and an underburnt relict (UBR); MIC-type (b), showing carbonate micritic aggregate (CA) and fossils (FS); MST-type (c), showing an aggregate composed of mono- (mQz) and polycrystalline quartz (pQz), pyroxene (Px), and chert fragments (Ch).
Figure 4. Representative microphotos of the three petrographic groups. CP-type (a), showing fragments of cocciopesto A (cpA) and cocciopesto B (cpB), a large lime lump (LL) and an underburnt relict (UBR); MIC-type (b), showing carbonate micritic aggregate (CA) and fossils (FS); MST-type (c), showing an aggregate composed of mono- (mQz) and polycrystalline quartz (pQz), pyroxene (Px), and chert fragments (Ch).
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Figure 5. XRPD spectra of representative mortars of (a) MST-type and (b) CP-type mortars.
Figure 5. XRPD spectra of representative mortars of (a) MST-type and (b) CP-type mortars.
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Figure 6. Point dispersion plot of the relationship between CaO and SiO2. In the red circle, samples belonging to CP group.
Figure 6. Point dispersion plot of the relationship between CaO and SiO2. In the red circle, samples belonging to CP group.
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Figure 7. Elemental maps (SEM-EDS) of representative samples of the three mortar types and corresponding spectra: elemental map of MIC-type mortar ((a) sample MSL10) and summary spectrum (b); elemental map of CP-type mortar ((c1) sample MSL12) and MST-type mortar ((c2) sample MSL12); representative spectrum of CP-type mortar ((d) sample MSL12, raster C12B2) and MST-type mortar ((e) sample MSL12, raster C12B8). The green line in c1–c2 denotes the surface between CP-type mortar (c1) and MST-type mortar (c2). Abbreviations on elemental maps: CA = carbonate aggregate; CP = cocciopesto, Qt = quartz; Px = pyroxene).
Figure 7. Elemental maps (SEM-EDS) of representative samples of the three mortar types and corresponding spectra: elemental map of MIC-type mortar ((a) sample MSL10) and summary spectrum (b); elemental map of CP-type mortar ((c1) sample MSL12) and MST-type mortar ((c2) sample MSL12); representative spectrum of CP-type mortar ((d) sample MSL12, raster C12B2) and MST-type mortar ((e) sample MSL12, raster C12B8). The green line in c1–c2 denotes the surface between CP-type mortar (c1) and MST-type mortar (c2). Abbreviations on elemental maps: CA = carbonate aggregate; CP = cocciopesto, Qt = quartz; Px = pyroxene).
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Figure 8. Elemental map (SEM-EDS) of a portion of sample MSL12, representative of CP-type mortar and including cocciopesto fragments (a). EDS spectrum of raster C12C1, showing the cocciopesto composition (b). Line scan (yellow line) of the interface area between cocciopesto and binder, showing the Al, Si, and Ca trends (c).
Figure 8. Elemental map (SEM-EDS) of a portion of sample MSL12, representative of CP-type mortar and including cocciopesto fragments (a). EDS spectrum of raster C12C1, showing the cocciopesto composition (b). Line scan (yellow line) of the interface area between cocciopesto and binder, showing the Al, Si, and Ca trends (c).
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Figure 9. SEM images (SE, (a)) of sample MSL12, whose surface showed a red painted layer; EDS spectra acquired in two areas with a red layer ((b) A3; (c) A7), both characterized by the presence of Fe.
Figure 9. SEM images (SE, (a)) of sample MSL12, whose surface showed a red painted layer; EDS spectra acquired in two areas with a red layer ((b) A3; (c) A7), both characterized by the presence of Fe.
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Figure 10. Microphotographs of mortar MST in sample MSL03, showing a sand composed of pyroxene (Px), chert, mono- (mQt), and polycrystalline quartz (pQz) fragments (a) and chert (Ch) fragments; polycrystalline quartz with strongly undulous extinction in sample MSL11 (b); pebble of marble in sample MSL09 showing calcite crystals with low-interference colors (c); pebble of marble with calcite crystals with high-interference colors in sample MSLC03 (d).
Figure 10. Microphotographs of mortar MST in sample MSL03, showing a sand composed of pyroxene (Px), chert, mono- (mQt), and polycrystalline quartz (pQz) fragments (a) and chert (Ch) fragments; polycrystalline quartz with strongly undulous extinction in sample MSL11 (b); pebble of marble in sample MSL09 showing calcite crystals with low-interference colors (c); pebble of marble with calcite crystals with high-interference colors in sample MSLC03 (d).
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Figure 11. Sketch of mortar in thin-section of samples MSL11 (a) and MSL03 (b); microphotographs of sample MSLC03, showing the clear contact surface between CP-type and MST-type mortars (c) and the red painting layer (20–100 µm) over the MST mortar (d).
Figure 11. Sketch of mortar in thin-section of samples MSL11 (a) and MSL03 (b); microphotographs of sample MSLC03, showing the clear contact surface between CP-type and MST-type mortars (c) and the red painting layer (20–100 µm) over the MST mortar (d).
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Table 1. Description, type of pebble pavement (where visible), building phase, and applied analytical methods for each sample.
Table 1. Description, type of pebble pavement (where visible), building phase, and applied analytical methods for each sample.
SampleMaterialMortar StratigraphyPavement TypeBuilding PhaseAnalitical Methods
OMXRPDXRFSEM-EDS
MSL01MortarNot layered4Templexxx-
MSL02Mortar, red paintingNot layered4Templexxx-
MSL03Pebble, mortar, red paintingLayered3Templex---
MSLC03Pebble, mortar, red paintingLayered3Templex---
MSL04Pebbles, mortar, red paintingNot layered3Before the building of the basilica xxx-
MSL05MortarNot layered4Basilicaxxx-
MSL06MortarNot layered1Unknownxxx-
MSL07MortarNot layered1Unknownxxx-
MSL09Mortar, PebbleNot layered2Unknownx---
MSL10MortarNot layered-Unknownxxxx
MSL11Mortar, red paintingLayered3Templexxx-
MSL12Mortar, red paintingNot layered-Unknownxxxx
Table 2. Included samples and peculiar features of matrix, aggregate, and porosity of each petrographic groups.
Table 2. Included samples and peculiar features of matrix, aggregate, and porosity of each petrographic groups.
GroupSubgroupSamplesBinderAggregatePore Roundness
CP-MSL01, MSL02, MSL03_A, MSLC03_B, MSL04, MSL07, MSL11_B, MSL12Variable-texture binder, underburnt relicts, lime lumpsCocciopesto A, cocciopesto B, mono- and polycrystalline quartz, pyroxenes, lithic fragmentsAngular
MICMIC1MSL05HomogeneousMicritic fragmentsRounded
MIC2MSL06, MSL10HomogeneousMicritic fragments, fossilsRounded
MST-MSL03_B, MSLC3_A, MSL11_AVariable-texture binder, lime lumpsChert fragments, limestone fragments, mono- and polycrystalline quartz, feldspars, pyroxenes, amphiboles Angular and rounded pores (very rare)
Table 3. Semiquantitative results of mineralogical composition obtained by XRPD analysis (Cal = calcite; Qt = quartz; Kfs = K-feldspar; Ill-Ms = illite–muscovite; Di = diopside; Gh = gehlenite. Abbreviation key: - = non-detectable; tr = traces; 1–5 = relative amounts (considered on the basis of the relative intensity of peaks: 1 ≤ 10%; 2 = 10–30%; 3 = 30–50%; 50–70%; 5 ≥ 70%).
Table 3. Semiquantitative results of mineralogical composition obtained by XRPD analysis (Cal = calcite; Qt = quartz; Kfs = K-feldspar; Ill-Ms = illite–muscovite; Di = diopside; Gh = gehlenite. Abbreviation key: - = non-detectable; tr = traces; 1–5 = relative amounts (considered on the basis of the relative intensity of peaks: 1 ≤ 10%; 2 = 10–30%; 3 = 30–50%; 50–70%; 5 ≥ 70%).
SampleCalQtKFsIll-MsDiGh
MSL01431tr-tr
MSL02431trtr-
MSL0551trtr--
MSL065tr-tr--
MSL0753trtr--
MSL104tr1tr--
MSL12431trtrtr
Table 4. Elemental compositions (% wt.) for samples analyzed by XRF.
Table 4. Elemental compositions (% wt.) for samples analyzed by XRF.
SampleSiO2TiO2Al2O3Fe2O3MgOMnOK2ONa2OCaOP2O5LOI
MSL0125.270.386.373.032.480.071.030.2333.850.1827.11
MSL0224.230.355.712.771.530.071.670.2635.750.2127.46
MSL056.310.091.820.580.900.040.190.0750.670.1139.21
MSL0612.080.143.181.401.010.051.350.3244.830.1335.51
MSL0725.150.163.151.511.100.070.970.2735.080.1335.41
MSL109.890.112.731.170.950.061.140.2746.530.1337.02
MSL1224.880.376.403.021.650.071.570.7134.450.1326.76
Table 5. Mean values and standard deviations (italics) of EDS analyses of the binder portion of each mortar type (MSL10 sample, A area, for MIC-type mortar; MSL12 sample, B1 area, for MST-type mortar; MSL12 sample, B2 area, for CP-type mortar). In parentheses: number of raster analyses (n). Full data are reported in the general table in Supplementary Material (Table S2). Percentages are normalized to 100.
Table 5. Mean values and standard deviations (italics) of EDS analyses of the binder portion of each mortar type (MSL10 sample, A area, for MIC-type mortar; MSL12 sample, B1 area, for MST-type mortar; MSL12 sample, B2 area, for CP-type mortar). In parentheses: number of raster analyses (n). Full data are reported in the general table in Supplementary Material (Table S2). Percentages are normalized to 100.
SampleAreaNa2OMgOAl2O3SiO2P2O5SO3ClK2OCaOTiO2MnOFe2O3
MSL10A (n = 11)0.781.367.1730.260.000.420.212.8854.440.180.002.30
0.310.461.684.480.000.410.180.638.300.320.000.99
MSL12B1 (n = 7)0.541.294.1918.090.000.090.161.2473.640.000.000.74
0.260.562.8210.730.000.250.220.8814.000.000.000.74
MSL12B2 (n = 3)0.621.416.1536.850.000.000.211.3150.870.000.002.58
0.230.220.4413.390.000.000.190.0413.970.000.000.28
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Fioretti, G.; D’Alessio, A.; Eramo, G. Archaeological Stratification in the St. Leucio Basilica (2nd Century BCE–6th Century CE, Canosa di Puglia, Southern Italy): Archaeometric Analysis of Pebble Pavements. Heritage 2025, 8, 186. https://doi.org/10.3390/heritage8060186

AMA Style

Fioretti G, D’Alessio A, Eramo G. Archaeological Stratification in the St. Leucio Basilica (2nd Century BCE–6th Century CE, Canosa di Puglia, Southern Italy): Archaeometric Analysis of Pebble Pavements. Heritage. 2025; 8(6):186. https://doi.org/10.3390/heritage8060186

Chicago/Turabian Style

Fioretti, Giovanna, Alessandro D’Alessio, and Giacomo Eramo. 2025. "Archaeological Stratification in the St. Leucio Basilica (2nd Century BCE–6th Century CE, Canosa di Puglia, Southern Italy): Archaeometric Analysis of Pebble Pavements" Heritage 8, no. 6: 186. https://doi.org/10.3390/heritage8060186

APA Style

Fioretti, G., D’Alessio, A., & Eramo, G. (2025). Archaeological Stratification in the St. Leucio Basilica (2nd Century BCE–6th Century CE, Canosa di Puglia, Southern Italy): Archaeometric Analysis of Pebble Pavements. Heritage, 8(6), 186. https://doi.org/10.3390/heritage8060186

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