LATE ROMAN METALLURGY IN CASTRO OF EL CASTILLÓN (SANTA EULALIA DE TÁBARA, ZAMORA) JOSE CARLOS SASTRE BLANCO AND PATRICIA FUENTES MELGAR 1. IntroductionCastro of El Castillón (Santa Eulalia de Tábara, Zamora), is situated on theborders of the Esla river, in the province of Zamora, less than a kilometerto the southwest of the Puente Quintos. This hillfort is located on a smallhill in the right border of Esla river, in a narrowing of the river channel.The archaeological site is located in the farm Dehesa de Tardajos, near tothe village of Santa Eulalia de Tábara, in the municipal region ofMoreruela de Tábara (Zamora). The altitude of the site oscillates between740 m and 749 m, and its geographical coordinates are 41º51´20” Northand 5º47´25” West. It has an approximate surface of 3ha and a walledperimeter of about 600 m. This walled perimeter provides a unique line ofdefense that surrounds the establishment, except in the East where there isa deep cliff. El Castillón began in the Bronze Age. We identified a small place withSchematic Art Rock located in this castro. This place was identified in1987 by Fernández Rivera like Abrigo de El Castillón (Fernández Rivera,1987; Sastre Blanco, 2006). The last historical evidence is from the LateRoman period, with the wisigothic arrival to the Iberian Peninsula in theIV-VI c. AD. Dating has been possible for the archaeological excavationsconducted between 2007 and 2009.
230 Late Roman Metallurgy in Castro of El Castillón 2. El Castillón and the Historical Context of the Late Roman Period in the Region of Tábara (Zamora)The Castillón has a privileged location, controlling the Esla river and nextto the Rroman way Vía de la Plata parallel to its left border. In the Romanperiod El Castillón was in the Conventus Asturum. The Esla river orÁstura (in Roman period) would serve to delimit between the populationsastures and vacceos. Vía de la Plata was a route parallel to the Esla riverthat connected the Roman cities Asturica Augusta (Astorga) with EmeritaAugusta (Merida). This was an important route for metal circulation fromthe mines of the northwest peninsula. Ancient sources see this route like adouble way with its center in Ocelondurii. In this place there were tworoutes, one to Asturica Augusta (Astorga) and another one to Caesaraugusta(Zaragoza). At the hillfort of El Castillón, the section of the Vía de la Plata thatcrosses this area is the section from Vico Aquario to Brigeco orBrigaecium. Vico Aquario is one of the mansions mentioned in the Itinerary ofAntonino and in Anonymous of Ravenna. Many author locate VicoAquario in Castrotorafe (Riego del Camino), situated to the south of ElCastillón. In the village of Castrotorafe there are only a few remains of anold medieval castle, but the occupation of this region dates from pre-roman time (during a visit to this castle we found a small piece of potterywith celtiberic decoration, now located in the Museum of Zamora). El Castillón is situated in a privileged place of communications,between two possible mansions of the Vía de la Plata, Vico Aquario to thesouth and Pretorion to the north. But it is possible to emphasize anotherimportant archeological site near El Castillón, only about 7 km to thesouth of El Castillón, this site is the Dehesa de Misleo (Sevillano Carvajal,1978). In Dehesa de Misleo evidence was found ranging from pre-Roman toEarly Medieval times. The most represented periods in Dehesa de Misleoare the Roman and Wisigothic periods. This archaeological site has stillnot been excavated, but fabulous pieces have been recovered throughfortuitous findings. A small treasure hoard from the Roman period wasdiscovered with more than 200 coins, including some from the Augustusperiod to Gallienus and Claudius II the Gothic. In this site a Romancemetery was located which included a very important deposit withOmega fibulae, rings, cases of bronze daggers, etc. These remains arefrom the II-III c. AD (Pérez Centeno, 1990).
Jose Carlos Sastre Blanco and Patricia Fuentes Melgar 231 To the south of the Castro of El Castillón, in the left border of the Eslariver we had one of the most important archeological sites from the LateRoman period in the province of Zamora. The Cristo de San Estebán(Muelas del Pan) has numerous similarities with El Castillón, mainly thestamped pottery and the Terra Sigillata Hispanica tardía (TSHt).Numerous remains from the Iron Age until the Late Roman period werefound at this archaeological site (Domínguez Bolaños, 993) 3. Archaeological Research in El CastillónThe first reference to the hillfort of El Castillón was in 1970, from VirgilioSevillano in his investigatión about the province of Zamora: Archaeologicaltestimonies of the province of Zamora. The first surveys of this site foundan enclosure fortified in a ‘U’ form, with three accesses/gates in the wall.In the interior of this site were the circular and rectangular structures, inmany areas altered by the presence of corrals and shepherd huts. Thishouse used some stones from the wall for its construction. In surveys, Esparza Arroyo found different materials such as ironslags, glasses, and abundant pieces of pottery, expecially late TerraSigillata Hispanica (TSHt), but no evidence of the Iron Age. The firsttheory about this Castro was as a site from the Late Roman period, IV-VBC, with no evidence before this period. (Esparza Arroyo, 1986). In 2007 a new archaeological project about preRoman and Late Romanhistory in the province of Zamora began, under the denomination:Archaeological Project of Research and Diffusion of the ProtohistoricalHeritage of the province of Zamora (P.I.D.P.A.D.Z.), with the firstexcavations in El Castillón directed by Jose Carlos Sastre Blanco(Universidad de Granada) and Oscar Rodriguez Monterrubio (UniversidadAutónoma de Madrid) (Rodriguez Monterrubio and Sastre Blanco, 2008). The survey works inside El Castillón documented 11 possible circularstructures of 4x1.90 m in diameter to the West and three possiblerectangular structures of 13.30x7.76 m located to the East. El Castillón has three different accesses or gateways in the enclosure.The most important of these accesses is in the Western area and is themain entrance. Another access is in the North-East area, descending to theEsla river. The third access is to the South. The defensive wall is morethan 4 meters in width, and approximately 10 meters in height. Theconstruction technique was very simple - great rectangular stones ofquartzite were used, without using mortar. The main access was reinforcedby two casamatas, one to each side of the gateway, and a smallrectangular entrance tower in the right of this gateway.
232 Late Roman Metallurgy in Castro of El Castillón The three campaigns of excavations undertaken in 2007, 2008 and2009 concentrated on the excavation of the zone to the West of the wall,on two circular structures located to the North of the castro, in relation tometallurgical works and the residential area and of storage located in thecentral zone of El Castillón, where the most significant remains werelocated; a bronze osculatorium. Different remains from excavations have a chronology that includesthe Iron Age, as demonstrated by small pottery fragments made by hand,to Late Roman-Wisigothic period (IV-VI c. AD), as demonstrated mainlyby stamped gray pottery.Figure 1. Rectangular structure related to a storehouse. 4. Metallurgical WorksIn the archaeological excavations of 2007 and 2008, an oval structurealmost totally related to metal work was excavated. This structure hasconvergent walls and a small entrance 40 centimeters in width, with twogreat vertical quartzite blocks at either side. In relation to the structure andthe numerous iron slags obtained in its interior, we can suppose that it is afurnace and that this zone of El Castillón was dedicated to metallurgical
Jose Carlos Sastre Blanco and Patricia Fuentes Melgar 233works, therefore demonstrating the analyses made in relation to iron slagsby the Department of Science of the Materials and MetallurgicalEngineering of Faculty of Chemical Sciences of the UniversidadComplutense de Madrid.Figure 2. Oval structure, excavated during 2007 and 2008, related to metallurgicalarea.The metellic remains found in El Castillón are not iron slags (ironsilicates) from furnaces for reduction of the iron. Instead, they are fromfragments for the forge and the steel cooled by the air. It has been possibleto deduce that they were smooth steel and of low carbon content, andthese high quality pieces suggest the presence of well-qualifiedblacksmiths. Ringwoodita is also present in the iron slags; Cáceres is theonly place in the Iberian Peninsula in which this mineral is found. Thisindicates commercial interaction between El Castillón and the Vía de laPlata. The archaeological excavation from 2008 documented 469 iron slagfragments with a gross weight of 13.930 kg.Metallic remains from El Castillón.The metallic material from El Castillón discovered from 2007 to 2009 wasdivided according to metallic composition; bronze, iron and copper, with aspecial section for the iron slags.Bronze artefacts:
234 Late Roman Metallurgy in Castro of El CastillónOsculatorium: It was discovered in El Castillón in 2008. Thisosculatorium is an important new find within the investigation of the LateRoman period in the Iberian Peninsula. This osculatorium was discoveredin a very clear archaeological context, perfectly delimited, and there canbe no doubt about its archaeological interpretation. In similar cases in theIberian Peninsula where these objects have been discovered in LateRoman tombs, there was not a lot of information about the real use of thisobject. Other osculatoria were discovered in survey works, withoutarchaeological context, and some were recovered from the Rastro ofMadrid (flea market). The osculatorium from El Castillón was discovered in a cleararchaeological context, inside a room which was excavated in 2008 and2009. This room may have been a storehouse, as a great amount of potterysuch as pots, bowls, jars, plates, and large earthen jars or dolias werediscovered. The osculatorium discovered in El Castillón is in an excellent state ofconservation as it is complete. It consists of three perfectly differentiatedparts - ring, stick and head (the decorated area). It was make using a mold,with an alloy of copper, tin, lead and zinc. Its overall length is 112 mm. The ring of this osculatorium is circular, with a diameter of 22 mm.The ring was formed using a small-flattened sheet, which gives it a fragileconsistency.Figure 3. Osculatorium found in Castro of El Castillón (Santa Eulalia de Tábara,Zamora) in 2008.
Jose Carlos Sastre Blanco and Patricia Fuentes Melgar 235 The stick is made up of an extended piece, convex in its central part,narrowing where it is united with the stick and the head (we mustremember that it is a massive piece, made using a mold, and that for thatreason it consists of only one piece and not three). This stick is 70 mm inlength. Perhaps the most interesting part of the osculatorium is the head, sinceit is what makes this piece unique. In the case of the osculatorium from ElCastillón the head is made up of a pair of birds (possibly doves) facingeach other, united at the tip. These birds are placed on a small pedestal.The anatomical characteristics of these birds are very noticeable, smallincisions were used to mark the plumage, the tip and the eyes. This type of artefact is relatively common, although to date only a fewhave been located within an archaeological context. We can mention someof the most interesting cases of all those found in the Iberian Peninsula,like Simancas (Valladolid), Las Merchanas (Salamanca), Las Pizarras(Segovia), Suellacabras (Soria), Clunia (Burgos), Merida (Badajoz), laTorrecilla (Madrid), Segobriga (Cuenca), Carpio de Tajo (Toledo), Azúa(Alava), Montefrio (Granada), etc. indicating an ample dispersion of thistype of artefact.Figure 4. Detail of the head of osculatorium, with the two birds united by the tip.Earring: One of the more interesting bronze artefacts which has beenfound a fine circular earring. This slope was found in the area of the houseused as a storehouse. This object is currently being analysed.
236 Late Roman Metallurgy in Castro of El CastillónHandle: During the 2008 excavation, a bronze artefact associated with acircular handle fragment was recovered. It was recovered in the areanominated as the metallurgical zone. We have not been able to ascertain ifit corresponds with an object made in the furnaces, or is an artefact relatedto the metalwork.Bronze tweezers: Another one of the bronze artefacts recovered in thecastro of El Castillón were tweezers of Roman typology. As this wasdiscovered during the 2009 excavation, analysis is ongoing so no furtherdata is available at present.Copper artefacts:Washers: A small washer or copper clasp of reduced dimensions. It wasfound inside one of the ovoid structures related to the furnaces. It is theonly copper piece documented from the site at present.Figure 5. Bronze tweezers recovered during the archaeological excavations of year2009.Iron artefacts:Nails: Nails are one of the more common metallic artefacts found in ElCastillón. The majority of them are of great size, with a noticeable head.Most were found in the housing area, in relation to some of the threestructures documented up to this point. They appear generally inarchaeological contexts associated with the ceiling of the house, thoughsome could also belong to doors or windows of these rooms. Perhaps themost remarkable nail is the one which appears to be associated with the
Jose Carlos Sastre Blanco and Patricia Fuentes Melgar 237bronze osculatorium, suggesting the possibility that the artefact may havebeen hung on this nail at the time of the rooms’ collapse.Striker pins: During the excavations of 2007 two extended striker pinswere located in the house zone. These iron striker pins were placed inareas determined to be the outer area of the houses. These areas have notyet been excavated, hence we cannot determine if they would be related tosome artisan utility.Knives: Until now two knives have been recovered, one during the 2008excavation and one during the 2009 excavation. Both are made of iron andare small in size. One was found in the metallurgical zone and the other inthe zone of houses. Regarding the knife from the metallurgical zone, wehave not been able to determine if it would have some function related tothe treatment of the metal. The knife from the housing area wasdiscovered in a storehouse room.Handles: Only one fragment of iron handle has been located up to thispoint. This was found during the 2009 excavation and as of now study isongoing. Nevertheless, we can say that it is an iron handle, of small size,corresponding to a container of small dimensions.Slags: The majority of slags discovered in the excavations of 2007 and2008 were found in the metallurgical zone. During the 2008 excavation,469 fragments of slag were gathered in this area. The total weight of thisslag is 13.930 kg, which shows us the importance of the slag within thefindings of the Castillón, and the importance of the metallurgic work in ElCastillón. 5. Metallurgical Analysis of Different Metals from El Castillón.First we must give thanks to Professor Antonio J. Criado Portal and theDepartment of Science of the Materials and Metallurgical Engineering ofthe Group of Investigation of Technology Mechanic and Arqueomateralia ofUniversity Complutense of Madrid, for the analysis of all the metallicpieces recovered during these excavations and for their collaboration withthe Archaeological Project of Research and Diffusion of the ProtohistoricalHeritage of the Province of Zamora (P.I.D.P.A.D.Z.). It was decided to analyse the metallic artefacts which were in a betterstate of conservation, and which, in our opinion, could offer better results.
238 Late Roman Metallurgy in Castro of El Castillón We used varying techniques to study and analyse the metallic artefacts,with Radiology only been used in the case of the osculatorium. Thetechniques employed were: - Sweep Electronic Microscope (M.E.B.). - Conventional Optical Microscopy. - X -Ray Diffraction. - Radiology In the case of the osculatorium, the following results were obtained. Itis a bronze piece with several alloy artefacts - tin, lead and zinc. The X-Ray Diffraction identified the tin bronze. It was possible to obtain an image by Sweep Electronic Microscope –the gray tonality against the segregations of whiter color indicates artefactsheavier than the copper, ie tin, lead and zinc.Figure 6. Image of the X-Ray realises to osculatorium discovered in Castro of ElCastillón (Santa Eulalia de Tábara, Zamora). It was possible to identify four characteristic zones that have beenanalyzed; the analysis of a general zone (1), shows the global compositionof the bronze of the osculatorium, ie. Cu: 87´2%; Sn: 4´8%; Pb: 5´3%; Zn:2´6%. The analysis of the zone (2), gave the following composition: Cu:19´3%; Pb: 80´7%, in which the high percentage of lead indicates to usthat it is a microsegregation of lead since this artefact is not soluble incopper; whereas the low percentage found in copper can be due to the firsteffect.
Jose Carlos Sastre Blanco and Patricia Fuentes Melgar 239 The analysis of (3) offers the following composition: Cu: 32´38%; Pb:67´6%. As in the case of the previous zone (2), it is another leadsegregation with a first effect of copper. Finally, the analysis of the zone indicated as (4) gave the followingcomposition: Cu: 92´7%; Sn: 5´33%; Zn: 1´97%, being a very smallsegregation, the first effect is very great, the reason why this compositionis similar to the matrix but with the lead absent.Figure 7. Micrography of osculatorium by Conventional Optical Microscopy(X500). The zinc present is of little importance in these bronzes, since it doesnot change mechanical characteristics. It gives a yellower color to thebronze and improves its ability. The presence of these segregations fills up the interdendritic spacesduring the solidification. The x-rays show that what was obtained was apiece without internal defects. Also, the x-rays indicate that the corrosionvisible is very superficial and there are no punctures in the osculatorium.The marks on the surface were produced after the moulding by mechanicalengraving. We can also make reference to the analysis of other metallic piecesfrom El Castillón. The washer or clasp of copper, which during excavationappeared to be made of bronze, was later determined to be copper. This isthe only copper piece recovered up to this point in the ongoing excavation.
240 Late Roman Metallurgy in Castro of El CastillónFigure 8. Laboratory Universidad Complutense de Madrid. It measures 1.5x2 cm and was identified as copper using X-Raysdiffraction and the analysis of Energies Dispersives (EDS-EDX). Thestudy of difractograma, besides showing that it is copper of great purity,detected particles such as silicates had adhered to it. The micrographsobtained by Sweep Electronic Microscope demonstrated that it was forgedin cold temperatures. Regarding the fragment of iron handle, the study of Sweep ElectronicMicroscope indicated that it is very smooth steel, with carbon contentinferior to 0.1% in mass. Microstructure shows steel made up of littlehomogenous ferrite grains with small aged pearlite colonies. The aging ofpearlite is the result of the passage of time. A small iron knife was also analysed. Metalographic study demonstratedthat it was warmed up intentionally to obtain a greater hardness.Micrographic obtained by means of Sweep Electronic Microscope a non-circular structure is observed corresponding with a steel that has beentempered. It was forged using heat and, later, cooled in water. The acicularferrite appears with secreted iron carbide multitude in its interphases, aproduct of the natural aging through time. One did not temper withmartensite, which had hardened the piece much more; since its carboncontent must go up to around 0.15% in mass.
Jose Carlos Sastre Blanco and Patricia Fuentes Melgar 241Figure 9. X-Rays diffraction analysis of osculatorium. Of the numerous nails recovered in El Castillón, the best two wereanalysed. The first is a very smooth steel nail, with a carbon contentinferior to 0.1% in mass, forged in heat and cooled in air. It is a ferriticmatrix, with some small pearlite colonies very aged in the grainboundaries. The other nail is very smooth steel, with a carbon content inferior to0.1% in mass. Observed in the micrographs, obtained by Sweep ElectronicMicroscope, is a very clean ferritic matrix of impurities, with somepearlite colonies very aged in the grain boundaries of ferrite and some verysmall idiomorphics iron carbides inside these grains. The steel was forged in heat and cooled in the air. This is evidenced inthe presence of those idiomorphics iron carbides inside the ferritic grains,which appeared by natural aging through time, as a result of a strongdegree of subcooling that supersaturated the ferrite. Also the aged anddegenerated pearlite demonstrates natural aging. Finally, with regard to the slags recovered in El Castillón, which arethe majority of the metallic materials found up to this point, we willconcentrate only on the analysis of slags gathered in 2007, since at themoment the corresponding analyses are being done for slags recovered in2008 and 2009.
242 Late Roman Metallurgy in Castro of El Castillón Most of the slags are composed of iron silicates very contaminated bythe soils there were located in. Some slags were found that did not comefrom furnaces of iron reduction. The study of the structure of the steel fragments,that still had a metallicnucleus, has been able to determine that it would be smooth steel, of lowcontent in carbon, hipoeutactoides (0.1% to 0.2% of carbon in mass),forged in heat and cooled by air. The content of impurities was correct forgood quality steel. This chemical composition and the correct use of theforge and its heat, suggests to us the presence of skilful blacksmiths whomanufactured good quality pieces.6. Conclusion about the Analysis of Bronze OsculatoriumFigure 10. Analysis of osculatorium by Sweep Electronic Microscope (M.E.B.)Analysis of bronze osculatorium by Sweep Electronic Microscope(M.E.B.), X-Rays diffraction, Conventional Optical Microscopy andRadiology, give us a complete information about a very interesting andimportant artefact in this historical period. Complete composition andmanufacture of this artefact is an indicative of the presence in the place ofprofessional blacksmith.
Jose Carlos Sastre Blanco and Patricia Fuentes Melgar 243 7. Metallurgic Composition of Bronze OsculatoriumElement App Intensity Weight% Weight% Atomic Conc. Corm. Sigma % OK 1.99 0.8304 2.22 0.35 8.70 Si K 0.30 0.4878 0.57 0.13 1.27 Cu K 91.28 1.0005 84.76 0.66 83.51 Zn K 2.82 1.0059 2.60 0.35 2.49 Sn L 4.15 0.8238 4.68 0.29 2.47 Pb M 3.86 0.6926 5.17 0.45 1.56 Totals 100.00 Weight %: Cu: 87,2%; Sn: 4,8%; Pb: 5,3%; Zn: 2,6%The bronze osculatorium has an important content in copper (87,2%), andan important content in lead (5,3%). Content in lead is very important forhardness of this artefact. The most interesting element discovered in the composition of theosculatorium by Sweep Electronic Microscope is zinc (2,6%). Zinc is onlyimportant in this composition for later engraving of this artefact. 8. ChronologyThe earliest remains from El Castillón are from the Iron Age, such assmall pieces of pottery and some remains discovered during the survey,and the Schematic Rock Art situated in a small cave next to this hillfort. The final occupation of El Castillon took place in the Late Romanperiod (IV-VI BC). We have a lot of references from this period, includingthe late Terra Sigillata Hispanica (TSHt) and stamp pottery. There areimportant references about this chronology, especially in el Cristo de SanEstebán (Muelas del Pan), in the south of El Castillón. The most important piece used to date this site is the bronzeOsculatorium. The only references to this type of artefact pertain to theLate Roman period, between centuries IV-VI AD. We have very clear and complete archeological contexts for thedifferent objects and structures at the site, but C-14 dating needs to beutilised to gain more specific dates. At the moment in the laboratories from Universidad Complutense deMadrid is analyzing by thermoluminescence different roofing tiles, bricks
244 Late Roman Metallurgy in Castro of El Castillónand adobes. With this analysis is possible have a important datation forthis archaeological site, and expecially comparation the dates fromthermoluminescence, with the dates from poterry or metals. 9. ConclusionsThe excavations from 2007 to 2009 have provided an important list ofmetallic materials, plus diverse structures related to metal work. Two oval structures excavated during 2007 and 2008 were proven torelate to the metal work, thanks to the structure and great amount of slagsrecovered inside the structures. The quality of steel studied demonstrated an excellent knowledge ofthe reduction processes to obtain the original pellets or lupias in thefurnaces. The examined steels are all of a great quality; the carbon content isvery low. All show strong natural aging, as is clear from the few presentpearlite colonies. According to the data collected up to now, we can speak of steel forgedin heat and cooled in the air, with the exception of one of the nails, whichwas cooled in water. The metallic object of most interest from all artefacts found up to thispoint is the bronze osculatorium, which was made using a mold. Theosculatorium is one of only a few pieces of this type that were found in aclear archaeological context, and unique in that it can be related tometallurgical structures. Although with the data that we have at themoment, it is not possible to conclusively determine that this piece wasmade here and not brought in from another place, it seems to us areasonable hypothesis. The objective for future excavations is to continue working in themetallurgical area, and to document the exact dimensions in all areas, thedifferent functions of the diverse structures, and the type of objects thatwere made at this site.