Sastre blanco & fuentes melgar[1]

New Perspectives on Late Antiquity

New Perspectives on Late Antiquity

Edited by

David Hernández de la Fuente

New Perspectives on Late Antiquity,
Edited by David Hernández de la Fuente

This book first published 2011

Cambridge Scholars Publishing

12 Back Chapman Street, Newcastle upon Tyne, NE6 2XX, UK

British Library Cataloguing in Publication Data
A catalogue record for this book is available from the British Library

Copyright © 2011 by David Hernández de la Fuente and contributors

All rights for this book reserved. No part of this book may be reproduced, stored in a retrieval system,
or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or
otherwise, without the prior permission of the copyright owner.

ISBN (10): 1-4438-2718-5, ISBN (13): 978-1-4438-2718-8

LATE ROMAN METALLURGY IN CASTRO
OF EL CASTILLÓN (SANTA EULALIA
DE TÁBARA, ZAMORA)

JOSE CARLOS SASTRE BLANCO
AND PATRICIA FUENTES MELGAR

1. Introduction
Castro of El Castillón (Santa Eulalia de Tábara, Zamora), is situated on the
borders of the Esla river, in the province of Zamora, less than a kilometer
to the southwest of the Puente Quintos. This hillfort is located on a small
hill 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 to
the village of Santa Eulalia de Tábara, in the municipal region of
Moreruela de Tábara (Zamora). The altitude of the site oscillates between
740 m and 749 m, and its geographical coordinates are 41º51´20” North
and 5º47´25” West. It has an approximate surface of 3ha and a walled
perimeter of about 600 m. This walled perimeter provides a unique line of
defense that surrounds the establishment, except in the East where there is
a deep cliff.
El Castillón began in the Bronze Age. We identified a small place with
Schematic Art Rock located in this castro. This place was identified in
1987 by Fernández Rivera like Abrigo de El Castillón (Fernández Rivera,
1987; Sastre Blanco, 2006). The last historical evidence is from the Late
Roman period, with the wisigothic arrival to the Iberian Peninsula in the
IV-VI c. AD. Dating has been possible for the archaeological excavations
conducted 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 next
to the Rroman way Vía de la Plata parallel to its left border. In the Roman
period El Castillón was in the Conventus Asturum. The Esla river or
Ástura (in Roman period) would serve to delimit between the populations
astures and vacceos. Vía de la Plata was a route parallel to the Esla river
that connected the Roman cities Asturica Augusta (Astorga) with Emerita
Augusta (Merida). This was an important route for metal circulation from
the mines of the northwest peninsula. Ancient sources see this route like a
double way with its center in Ocelondurii. In this place there were two
routes, 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 that
crosses this area is the section from Vico Aquario to Brigeco or
Brigaecium.
Vico Aquario is one of the mansions mentioned in the Itinerary of
Antonino and in Anonymous of Ravenna. Many author locate Vico
Aquario in Castrotorafe (Riego del Camino), situated to the south of El
Castillón. In the village of Castrotorafe there are only a few remains of an
old 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 pottery
with 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 the
south and Pretorion to the north. But it is possible to emphasize another
important archeological site near El Castillón, only about 7 km to the
south of El Castillón, this site is the Dehesa de Misleo (Sevillano Carvajal,
1978).
In Dehesa de Misleo evidence was found ranging from pre-Roman to
Early Medieval times. The most represented periods in Dehesa de Misleo
are the Roman and Wisigothic periods. This archaeological site has still
not been excavated, but fabulous pieces have been recovered through
fortuitous findings. A small treasure hoard from the Roman period was
discovered with more than 200 coins, including some from the Augustus
period to Gallienus and Claudius II the Gothic. In this site a Roman
cemetery was located which included a very important deposit with
Omega fibulae, rings, cases of bronze daggers, etc. These remains are
from 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 Esla
river we had one of the most important archeological sites from the Late
Roman period in the province of Zamora. The Cristo de San Estebán
(Muelas del Pan) has numerous similarities with El Castillón, mainly the
stamped pottery and the Terra Sigillata Hispanica tardía (TSHt).
Numerous remains from the Iron Age until the Late Roman period were
found at this archaeological site (Domínguez Bolaños, 993)

3. Archaeological Research in El Castillón
The first reference to the hillfort of El Castillón was in 1970, from Virgilio
Sevillano in his investigatión about the province of Zamora: Archaeological
testimonies of the province of Zamora. The first surveys of this site found
an 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, in
many areas altered by the presence of corrals and shepherd huts. This
house used some stones from the wall for its construction.
In surveys, Esparza Arroyo found different materials such as iron
slags, glasses, and abundant pieces of pottery, expecially late Terra
Sigillata Hispanica (TSHt), but no evidence of the Iron Age. The first
theory about this Castro was as a site from the Late Roman period, IV-V
BC, with no evidence before this period. (Esparza Arroyo, 1986).
In 2007 a new archaeological project about preRoman and Late Roman
history in the province of Zamora began, under the denomination:
Archaeological Project of Research and Diffusion of the Protohistorical
Heritage of the province of Zamora (P.I.D.P.A.D.Z.), with the first
excavations in El Castillón directed by Jose Carlos Sastre Blanco
(Universidad de Granada) and Oscar Rodriguez Monterrubio (Universidad
Autónoma de Madrid) (Rodriguez Monterrubio and Sastre Blanco, 2008).
The survey works inside El Castillón documented 11 possible circular
structures of 4x1.90 m in diameter to the West and three possible
rectangular 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 the
main entrance. Another access is in the North-East area, descending to the
Esla river. The third access is to the South. The defensive wall is more
than 4 meters in width, and approximately 10 meters in height. The
construction technique was very simple - great rectangular stones of
quartzite were used, without using mortar. The main access was reinforced
by two casamatas, one to each side of the gateway, and a small
rectangular entrance tower in the right of this gateway.


The three campaigns of excavations undertaken in 2007, 2008 and
2009 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 to
metallurgical works and the residential area and of storage located in the
central zone of El Castillón, where the most significant remains were
located; a bronze osculatorium.
Different remains from excavations have a chronology that includes
the Iron Age, as demonstrated by small pottery fragments made by hand,
to Late Roman-Wisigothic period (IV-VI c. AD), as demonstrated mainly
by stamped gray pottery.

Figure 1. Rectangular structure related to a storehouse.

4. Metallurgical Works
In the archaeological excavations of 2007 and 2008, an oval structure
almost totally related to metal work was excavated. This structure has
convergent walls and a small entrance 40 centimeters in width, with two
great vertical quartzite blocks at either side. In relation to the structure and
the numerous iron slags obtained in its interior, we can suppose that it is a
furnace and that this zone of El Castillón was dedicated to metallurgical


works, therefore demonstrating the analyses made in relation to iron slags
by the Department of Science of the Materials and Metallurgical
Engineering of Faculty of Chemical Sciences of the Universidad
Complutense de Madrid.

Figure 2. Oval structure, excavated during 2007 and 2008, related to metallurgical
area.

The metellic remains found in El Castillón are not iron slags (iron
silicates) from furnaces for reduction of the iron. Instead, they are from
fragments for the forge and the steel cooled by the air. It has been possible
to deduce that they were smooth steel and of low carbon content, and
these high quality pieces suggest the presence of well-qualified
blacksmiths. Ringwoodita is also present in the iron slags; Cáceres is the
only place in the Iberian Peninsula in which this mineral is found. This
indicates commercial interaction between El Castillón and the Vía de la
Plata. The archaeological excavation from 2008 documented 469 iron slag
fragments with a gross weight of 13.930 kg.

Metallic remains from El Castillón.
The metallic material from El Castillón discovered from 2007 to 2009 was
divided according to metallic composition; bronze, iron and copper, with a
special section for the iron slags.
Bronze artefacts:


Osculatorium: It was discovered in El Castillón in 2008. This
osculatorium is an important new find within the investigation of the Late
Roman period in the Iberian Peninsula. This osculatorium was discovered
in a very clear archaeological context, perfectly delimited, and there can
be no doubt about its archaeological interpretation. In similar cases in the
Iberian Peninsula where these objects have been discovered in Late
Roman tombs, there was not a lot of information about the real use of this
object. Other osculatoria were discovered in survey works, without
archaeological context, and some were recovered from the Rastro of
Madrid (flea market).
The osculatorium from El Castillón was discovered in a clear
archaeological context, inside a room which was excavated in 2008 and
2009. This room may have been a storehouse, as a great amount of pottery
such as pots, bowls, jars, plates, and large earthen jars or dolias were
discovered.
The osculatorium discovered in El Castillón is in an excellent state of
conservation as it is complete. It consists of three perfectly differentiated
parts - 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 fragile
consistency.

Figure 3. Osculatorium found in Castro of El Castillón (Santa Eulalia de Tábara,
Zamora) in 2008.


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 must
remember that it is a massive piece, made using a mold, and that for that
reason it consists of only one piece and not three). This stick is 70 mm in
length.
Perhaps the most interesting part of the osculatorium is the head, since
it is what makes this piece unique. In the case of the osculatorium from El
Castillón the head is made up of a pair of birds (possibly doves) facing
each other, united at the tip. These birds are placed on a small pedestal.
The anatomical characteristics of these birds are very noticeable, small
incisions were used to mark the plumage, the tip and the eyes.
This type of artefact is relatively common, although to date only a few
have been located within an archaeological context. We can mention some
of 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), la
Torrecilla (Madrid), Segobriga (Cuenca), Carpio de Tajo (Toledo), Azúa
(Alava), Montefrio (Granada), etc. indicating an ample dispersion of this
type 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 been
found a fine circular earring. This slope was found in the area of the house
used as a storehouse. This object is currently being analysed.


Handle: During the 2008 excavation, a bronze artefact associated with a
circular handle fragment was recovered. It was recovered in the area
nominated as the metallurgical zone. We have not been able to ascertain if
it corresponds with an object made in the furnaces, or is an artefact related
to the metalwork.
Bronze tweezers: Another one of the bronze artefacts recovered in the
castro of El Castillón were tweezers of Roman typology. As this was
discovered during the 2009 excavation, analysis is ongoing so no further
data is available at present.

Copper artefacts:
Washers: A small washer or copper clasp of reduced dimensions. It was
found inside one of the ovoid structures related to the furnaces. It is the
only copper piece documented from the site at present.

Figure 5. Bronze tweezers recovered during the archaeological excavations of year
2009.

Iron artefacts:
Nails: Nails are one of the more common metallic artefacts found in El
Castillón. 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 three
structures documented up to this point. They appear generally in
archaeological contexts associated with the ceiling of the house, though
some could also belong to doors or windows of these rooms. Perhaps the
most remarkable nail is the one which appears to be associated with the


bronze osculatorium, suggesting the possibility that the artefact may have
been hung on this nail at the time of the rooms’ collapse.

Striker pins: During the excavations of 2007 two extended striker pins
were located in the house zone. These iron striker pins were placed in
areas determined to be the outer area of the houses. These areas have not
yet been excavated, hence we cannot determine if they would be related to
some artisan utility.

Knives: Until now two knives have been recovered, one during the 2008
excavation and one during the 2009 excavation. Both are made of iron and
are small in size. One was found in the metallurgical zone and the other in
the zone of houses. Regarding the knife from the metallurgical zone, we
have not been able to determine if it would have some function related to
the treatment of the metal. The knife from the housing area was
discovered in a storehouse room.

Handles: Only one fragment of iron handle has been located up to this
point. This was found during the 2009 excavation and as of now study is
ongoing. 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 and
2008 were found in the metallurgical zone. During the 2008 excavation,
469 fragments of slag were gathered in this area. The total weight of this
slag is 13.930 kg, which shows us the importance of the slag within the
findings of the Castillón, and the importance of the metallurgic work in El
Castillón.

5. Metallurgical Analysis of Different
Metals from El Castillón.
First we must give thanks to Professor Antonio J. Criado Portal and the
Department of Science of the Materials and Metallurgical Engineering of
the Group of Investigation of Technology Mechanic and Arqueomateralia of
University Complutense of Madrid, for the analysis of all the metallic
pieces recovered during these excavations and for their collaboration with
the Archaeological Project of Research and Diffusion of the Protohistorical
Heritage of the Province of Zamora (P.I.D.P.A.D.Z.).
It was decided to analyse the metallic artefacts which were in a better
state of conservation, and which, in our opinion, could offer better results.


We used varying techniques to study and analyse the metallic artefacts,
with Radiology only been used in the case of the osculatorium. The
techniques 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. It
is 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 artefacts
heavier than the copper, ie tin, lead and zinc.

Figure 6. Image of the X-Ray realises to osculatorium discovered in Castro of El
Castillón (Santa Eulalia de Tábara, Zamora).

It was possible to identify four characteristic zones that have been
analyzed; the analysis of a general zone (1), shows the global composition
of 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 us
that it is a microsegregation of lead since this artefact is not soluble in
copper; whereas the low percentage found in copper can be due to the first
effect.


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 lead
segregation with a first effect of copper.
Finally, the analysis of the zone indicated as (4) gave the following
composition: Cu: 92´7%; Sn: 5´33%; Zn: 1´97%, being a very small
segregation, the first effect is very great, the reason why this composition
is 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 does
not change mechanical characteristics. It gives a yellower color to the
bronze and improves its ability.
The presence of these segregations fills up the interdendritic spaces
during the solidification. The x-rays show that what was obtained was a
piece without internal defects. Also, the x-rays indicate that the corrosion
visible is very superficial and there are no punctures in the osculatorium.
The marks on the surface were produced after the moulding by mechanical
engraving.
We can also make reference to the analysis of other metallic pieces
from El Castillón. The washer or clasp of copper, which during excavation
appeared to be made of bronze, was later determined to be copper. This is
the only copper piece recovered up to this point in the ongoing excavation.


Figure 8. Laboratory Universidad Complutense de Madrid.

It measures 1.5x2 cm and was identified as copper using X-Rays
diffraction and the analysis of Energies Dispersives (EDS-EDX). The
study of difractograma, besides showing that it is copper of great purity,
detected particles such as silicates had adhered to it. The micrographs
obtained by Sweep Electronic Microscope demonstrated that it was forged
in cold temperatures.
Regarding the fragment of iron handle, the study of Sweep Electronic
Microscope indicated that it is very smooth steel, with carbon content
inferior to 0.1% in mass. Microstructure shows steel made up of little
homogenous ferrite grains with small aged pearlite colonies. The aging of
pearlite is the result of the passage of time.
A small iron knife was also analysed. Metalographic study demonstrated
that 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 been
tempered. It was forged using heat and, later, cooled in water. The acicular
ferrite appears with secreted iron carbide multitude in its interphases, a
product of the natural aging through time. One did not temper with
martensite, which had hardened the piece much more; since its carbon
content must go up to around 0.15% in mass.


Figure 9. X-Rays diffraction analysis of osculatorium.

Of the numerous nails recovered in El Castillón, the best two were
analysed. The first is a very smooth steel nail, with a carbon content
inferior to 0.1% in mass, forged in heat and cooled in air. It is a ferritic
matrix, with some small pearlite colonies very aged in the grain
boundaries.
The other nail is very smooth steel, with a carbon content inferior to
0.1% in mass. Observed in the micrographs, obtained by Sweep Electronic
Microscope, is a very clean ferritic matrix of impurities, with some
pearlite colonies very aged in the grain boundaries of ferrite and some very
small idiomorphics iron carbides inside these grains.
The steel was forged in heat and cooled in the air. This is evidenced in
the presence of those idiomorphics iron carbides inside the ferritic grains,
which appeared by natural aging through time, as a result of a strong
degree of subcooling that supersaturated the ferrite. Also the aged and
degenerated pearlite demonstrates natural aging.
Finally, with regard to the slags recovered in El Castillón, which are
the majority of the metallic materials found up to this point, we will
concentrate only on the analysis of slags gathered in 2007, since at the
moment the corresponding analyses are being done for slags recovered in
2008 and 2009.


Most of the slags are composed of iron silicates very contaminated by
the soils there were located in. Some slags were found that did not come
from furnaces of iron reduction.
The study of the structure of the steel fragments,that still had a metallic
nucleus, has been able to determine that it would be smooth steel, of low
content 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 for
good quality steel. This chemical composition and the correct use of the
forge and its heat, suggests to us the presence of skilful blacksmiths who
manufactured good quality pieces.

6. Conclusion about the Analysis of Bronze Osculatorium

Figure 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 and
Radiology, give us a complete information about a very interesting and
important artefact in this historical period. Complete composition and
manufacture of this artefact is an indicative of the presence in the place of
professional blacksmith.


7. Metallurgic Composition of Bronze Osculatorium
Element 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%), and
an important content in lead (5,3%). Content in lead is very important for
hardness of this artefact.
The most interesting element discovered in the composition of the
osculatorium by Sweep Electronic Microscope is zinc (2,6%). Zinc is only
important in this composition for later engraving of this artefact.

8. Chronology
The earliest remains from El Castillón are from the Iron Age, such as
small 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 Roman
period (IV-VI BC). We have a lot of references from this period, including
the late Terra Sigillata Hispanica (TSHt) and stamp pottery. There are
important references about this chronology, especially in el Cristo de San
Estebán (Muelas del Pan), in the south of El Castillón.
The most important piece used to date this site is the bronze
Osculatorium. The only references to this type of artefact pertain to the
Late Roman period, between centuries IV-VI AD.
We have very clear and complete archeological contexts for the
different objects and structures at the site, but C-14 dating needs to be
utilised to gain more specific dates.
At the moment in the laboratories from Universidad Complutense de
Madrid is analyzing by thermoluminescence different roofing tiles, bricks


and adobes. With this analysis is possible have a important datation for
this archaeological site, and expecially comparation the dates from
thermoluminescence, with the dates from poterry or metals.

9. Conclusions
The excavations from 2007 to 2009 have provided an important list of
metallic materials, plus diverse structures related to metal work.
Two oval structures excavated during 2007 and 2008 were proven to
relate to the metal work, thanks to the structure and great amount of slags
recovered inside the structures.
The quality of steel studied demonstrated an excellent knowledge of
the reduction processes to obtain the original pellets or lupias in the
furnaces.
The examined steels are all of a great quality; the carbon content is
very low. All show strong natural aging, as is clear from the few present
pearlite colonies.
According to the data collected up to now, we can speak of steel forged
in heat and cooled in the air, with the exception of one of the nails, which
was cooled in water.
The metallic object of most interest from all artefacts found up to this
point is the bronze osculatorium, which was made using a mold. The
osculatorium is one of only a few pieces of this type that were found in a
clear archaeological context, and unique in that it can be related to
metallurgical structures. Although with the data that we have at the
moment, it is not possible to conclusively determine that this piece was
made here and not brought in from another place, it seems to us a
reasonable hypothesis.
The objective for future excavations is to continue working in the
metallurgical area, and to document the exact dimensions in all areas, the
different functions of the diverse structures, and the type of objects that
were made at this site.

Sastre blanco & fuentes melgar[1]

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