Why conduct new non-destructive surveys of known, excavated
sites?
The Celtic oppida of Bohemia are a representative of a particular type of extensive hillfort that originated in the late La Tène period, and which has been investigated in the form of usually prolonged, intensive archaeological excavations. The subsequent processing of such investigations of what are normally complex archaeological situations with a large number of artefacts has required, and will yet require, many years of intensive archaeological work. In terms of the areas of the oppida, only small fractions of the total have been subjected to detailed excavation. As it is unlikely, given costs, time constraints and required labour intensity, that these sites will ever be excavated in toto, it would seem to be appropriate to attempt complementary forms of the monitoring, survey, identification and assessment of whole localities. The application of modern, less financially demanding, non-destructive methods can now offer further opportunities for the systematic survey and research into hillforts, conducted in co-operation with archaeologists.
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Figure 1. Locations of Celtic oppida in Central and South Bohemia selected for non-destructive survey within the project.Click to enlarge.
The first systematically implemented wide-area surveys of selected hillforts in Bohemia were possible only after certain investments had been made in 1998 (Křivánek 2001c, 2003a) as part of the archaeological "Settlement Patterns in Prehistoric Bohemia" project, supported by the Grant Agency of the Czech Republic (1997-2002 - Gojda et al.). The advantages of wide-area geophysical measurements within fortifications with no structures surviving on the surface were proven by the outcome of the pioneer study in Bohemia on "The identification of destroyed fortifications and internal settlement structures at hillforts", conducted with the support of the Dept. of Monument Preservation of the Czech Ministry of Culture (Grant no. PK99P04OPP007 - Křivánek 1999-2000). The project results, applicable within both archaeology and heritage management (Křivánek 2000, 2001ab), demonstrated the validity of a new, fast and inexpensive method of detailed area survey for significant fortified archaeological sites.
The optimal methodological combination for the extensive and intensive survey of non-excavated parts of oppida would seem to be the use of wide-area geophysical survey along with other non-destructive techniques (such as surface survey, surface artefact collection). Their rapid and notably inexpensive results can play a critical role in the processes of monitoring site structure, evaluating large territorial units from previous archaeological excavations and more effectively protecting entire archaeological sites. The primary field method in the project is sufficiently detailed (yet nevertheless wide-area) geophysical survey of oppida selected on the basis of earlier surveys and excavations, sometimes undertaken on ploughed fields along with systematic surface artefact collection, the processing of historical maps and selective verification in the form of test pitting or employing the results of aerial archaeology (or the verification of significant new findings by microprobe under the supervision of archaeologists). The composition of the research team, and the anticipated contribution of the individual scientists and specialists (see below) reflects the nature of almost exclusively non-destructive wide-area survey of oppida as unique and specific sites.
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Figure 2. Photo-documentation of the old archaeological excavation of the Nevězice oppidum by Svoboda 1949-1951, outside the main rampart with outer ditch now located on arable fields.
SITE SELECTION
Celtic oppida commonly extend over up
to several dozen hectares of highly variable landscape (slopes, hills
and/or plains; wooded, grassy and/or ploughed; etc.). The selection of
appropriate terrain within an oppidum for wide-area survey should
be based on the archaeological data available and on a knowledge of the
site, its components and current state, all as determined by the
researcher and archaeologists involved in the project. It is therefore
necessary from the outset to respect the practical aspects of measurement
efficiency, and select propitious, suitable and accessible areas for
investigation, eliminating unacceptable areas, areas with a significant
intensity of recent activity (including earlier excavations) and areas
otherwise subject to disturbing influences. For the purposes of this
project, the following oppida in Central and South Bohemia were
selected (Figure 1).
Hrazany (Radíč cadastre, Příbram district).
The
oppidum is located in the area known locally as 'Na Hrádnici', on
the right bank of the Vltava river, next to the confluence with the
Mastník stream. The greater part of the site is on meadowland (former
fields), with some smaller parts in the surrounding woods. The overall
fortified area, including the baileys, runs to some 39 ha. Systematic
archaeological investigations were conducted by the Institute of
Archaeology in Prague in 1951-1963 (Jansová 1986, 1988, 1992; Drda &
Rybová 1997). Human activity on the site has been identified from as far
back as the Palaeolithic and Mesolithic periods, an Eneolithic settlement
and another settlement dating to the Bronze Age and Hallstatt period. The
oppidum is divided into an inner, central part (containing
farmsteads, iron-processing and smithing areas, and with four gates) and
two fortified baileys (with two further gates). The oppidum
(probably used from 120-50 BC) was destroyed by fire, restored, and
destroyed by fire again. The site has been proposed as a national heritage
monument.
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Figure 3. Aerial photography (by Gojda 2003) of the intensively ploughed-out central part of the Stradonice oppidum.
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Figure 4. Archaeological reconstruction (by Břeň 1966) of the western gate of the Ttřísov oppidum.
Nevězice (Písek district).
The oppidum is located
in the area known locally as 'Hrad' (lit. 'castle, stronghold'), on the
left bank of the Vltava river, above an indented stream mouth. The inner
parts of the site are on meadowland with some woods, while the outer parts
lie on arable fields. The fortified area covers around 13 ha. Survey and
rescue excavations were conducted here in 1949-1951 (Figure 2) and 1980
(Drda 1987; Drda & Rybová 1997); the earliest settlement identified
dates to the late Bronze Age. The inner area is undivided, and entry to it
is gained through double ramparts to the north-east; there is another gate
in the south-eastern part of the fortification and the slopes are
terraced. This oppidum was destroyed by fire.
Stradonice (Beroun district).
The oppidum is located
in the area known locally as 'Hradiště' (lit. 'hillfort'), west of the
village and above the confluence of the Berounka river and Habrový stream.
The larger, central part of the site lies on arable fields (Figure 3),
with a smaller area lying on meadows. The fortified area covers 90.3 ha.
Numerous finds including hoards of gold coins were obtained from the site
at the end of the nineteenth century. The first archaeological
investigations were conducted by Stocký in 1929, while rescue excavations
linked to the construction of a gas pipeline were undertaken by the Prague
Institute of Archaeology in 1981 and 1982-1984 (Rybová & Drda 1994;
Drda & Rybová 1997). The earliest settlement identified dates to the
Hallstatt period. Judging from the surviving stretches of the
fortifications, the oppidum can be divided into an inner area and
wide outer fortified zone (with craft workshops and a mint), originally
with 4 major gates. The oppidum was destroyed in the second half of
the first century BC. The site has been proposed as a national heritage
monument.
Třísov (Český Krumlov district).
The oppidum is
located in the area known locally as 'Hradiště - V hradišti' (lit.
'Hillfort - in the hillfort'), north of the village, in a meander of the
Vltava by the mouth of the Kremžský stream. The inner and outer parts
comprise recently ploughed fields or meadows (formerly fields), with the
peaks mainly in the surrounding woods. The fortified area covers some 26
ha. Systematic archaeological investigations were conducted by the
National Museum in Prague from 1954-1982 (Břeň 1966, 1975; Drda &
Rybová 1997). The oppidum is divided in two plataeus (hills) and an
extensive inner area (wooden structures - workshops) with a double
fortification system along the western side, and west (Figure 4) and east
gate. The oppidum, dating to the second half of the first century
BC, was abandoned after half a century, around the turn of the millennium.
The site is a national heritage monument.
Závist (Lhota cadastre, Prague-West & Prague -Točná
districts).
The oppidum is located on two hills known
locally as 'Hradiště' (lit. 'hillfort') and 'Ĺ ance' (lit. 'rampart')
on the left bank of the Vltava, above the former confluence with the
Berounka and the indented mouth of the Břežany valley. Most of the site is
covered by wood, but a large part of the fortified outer area is on arable
fields with a new residential development nearby. The fortified area
covers approximately 157 ha. Systematic archaeological investigation was
carried out by the Institute of Archaeology in Prague from 1963-1989
(Čižmář 1989; Motyková, Drda & Rybová 1984; Drda & Rybová 1993,
1997). A settlement on the site has been identified from as early as the
Eneolithic period, along with an extensive Bronze Age hill-fort and
intensive settlement of the Bylany culture, the late Hallstatt period and
the Early Middle Ages. The fortification shows numerous gates (13 known to
date) and is divided into an acropolis, internal settlements, external
settlements (baileys) and other components. Five main developmental stages
have been identified for the fortification. The oppidum dates to the
second to late first centuries BC. The site is a national heritage
monument.
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Figure 5. The magnetometric survey (approx. 3.2 ha; Křivánek 2003) at Nevězice distinguished concentrated anthropogenic activities, empty zones and geological changes in the inner part of the oppidum. Click to enlarge.
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Figure 6. Schematic plan of the Závist oppidum (Drda & Rybová 1997), showing the areas where geophysical surveys were conducted in 2003 until summer 2004. Click to enlarge.
PROBLEMS AND AIMS
The subjects addressed by the submitted
project for large scale non-destructive oppidum survey can be divided into
several related categories, with a varying view of the applicability of
the results. The results of the geophysical methods, originally associated
with the natural sciences but now interdisciplinary, will be applicable to
the resolution of partial (individual oppida) and general
archaeological expert issues, the recording and protection of significant
archaeological monuments and with respect to the methodological
presentation of new and unusual applications of geophysics to archaeology.
It is necessary that a suitable methodology is employed in the
non-destructive mapping within extensive non-excavated parts of
oppida areas over the course of the whole project, reflecting the
needs of the archaeologists particularly as regards wide-area geophysical
measurement (continuous result assessment for the most effective survey),
followed by other complementary non-destructive methods. The following may
be regarded as feasible project objectives:
2. The identification of other indistinct or non-preserved parts of fortification systems, of gates, of interior structures and/or of roads within selected grassy or wooded inner areas of oppida.
3. The identification of significant and resolvable structures not surviving on the surface, of their concentrations or the concentration of activities within the surveyed inner areas of oppida, and of presumed structures and activities outside the fortification.
4. Determination of the probable fortification (and/or structure) types and of their current states of sub-surface preservation (or of the scope of later and modern surface modifications and site adjustments to the archaeological contexts).
5. The preliminary or general dating of artefacts or diverse anthropogenic activities identified by geophysical investigation of arable or otherwise degraded areas by archaeologists (the processing of systematic surface artefact collection and surface survey assemblages, etc.).
6. Composition of general maps for the exact identification and registration of the sites, with the verification of other areas or internal structures of oppida for the adequate protection of the entire archaeological monuments.
7. Comparison of the results of non-destructive methods with current knowledge regarding the oppida based on archaeological investigation, the filling out of current information, new maps and possibly new interpretations of the use of individual areas within the sites.
8. An assessment of the benefits of, and further potential for, non-destructive surveys of the oppida, and of the common traits and specific features within individual sites.
SURVEY METHODS
The great advantage held by all modern and
often inter-disciplinary non-destructive archaeological survey methods is
that they can be applied without disturbing the archaeological features,
contexts, artefacts and/or natural environment of the sites concerned. The
primary project methodology is based on the wide-area geophysical
survey of selected locations. The major geophysical method applicable
on such a large scale is wide-area magnetometric survey, the magnetometry
being the most suitable geophysical method for the detection of diverse
sunken or burned archaeological features surviving beneath the surface. On
arable fields and meadows, as well as in wooded areas without low
vegetation, it is possible to identify sections of linear structures,
various fortification systems, and enclosures/fencing or other zoning
(dikes, trenches, palisades, channels, terraces, arable land) - including
areas of discontinuity (entrances, gates) - which do not survive on the
surface; it is also possible to distinguish larger and smaller sunken
isometric structures (houses, clay pits, postholes, graves etc.),
structures built of stone (houses, walls etc.), and various manufacturing
and burned features (furnaces, mine tailings, spoil heaps, smithies,
burned sections of fortifications etc.). On the basis of the geophysical
anomalies identified it is possible to make comparisons with other
wide-area measurements and traces settlement structure, the character of
anthropogenic activities within the oppida, and the current surface
preservation or disturbance to various situations and areas.
Since 1998 both detailed and wide-area magnetometric surveys of archaeological sites have been conducted using high sensitive, precise and powerful caesium magnetometers (Smartmag SM-4g model, Scintrex, Canada), with the possibility of making instant measurements of the local magnetic field. From previous experience and the results of geophysical surveys conducted at hill-forts and other fortified locations it may be expected that the project as designed (depending on the measurement density applied - e.g. 1x0.25m or 0.5x0.2 m with caesium magnetometers) is capable of investigating a total of some 30-60 ha (6-12 ha per year). Where more complex, detailed survey of partial situations and stony features would be appropriate geo-electrical apparent resistivity can be measured (using an RM-15 instrument by Geoscan Research, United Kingdom), as can electromagnetic apparent conductivity or magnetic susceptibility (using an EM-38b instrument by Geonics, Canada). The large anticipated volumes of measured geophysical data (usually running to several tens of thousands of points in a single day!) will be processed using the geophysical software Oasis-montaj (Geosoft, Canada), Envimap (Scintrex, Canada), Surfer (Golden software, USA) and Geoplot (Geoscan Research, United Kingdom).
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Figure 7. The magnetometric survey in the outer, wooded part (aprox. 1.1 ha; Křivánek 2003) of the Závist oppidum distinguished the sub-surface remains of 2 separate and previously unknown entrances through the outer multiple ditch and rampart fortification.
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Figure 8. The results of experimental magnetometric prospection in the 'Šance' area (approx. 0.45 ha; Křivánek 2003) of the Závist oppidum demonstrated the earlier, different use of this recently wooded area as arable fields. Click to enlarge.
Another non-destructive method used in the project is systematic surface artefact collection. On the arable parts of oppida (and e.g. beyond the perimeter established by the fortifications) geophysical survey results will be complemented by systematic surface survey conducted using a regular, uniform grid; it will be then possible to compare the distribution of artefacts with the interpretation of the geophysical research results. The artefacts collected during surface survey will be evaluated by archaeologists. The grids used for geophysical investigation, artefact collection etc. will be localised using GPS (e.g. a Trimble Pathfinder GPS unit). Where new archaeological situations are identified that no longer survive on the surface, it is also possible to employ a complementary detailed vertical geodetic survey to obtain a detailed vertical model of the terrain. Another complementary and almost non-destructive method that can be used at selected points chosen on the basis of the geophysical survey results is test pitting. The likely presence of metal artefacts on intensively ploughed fields will also be verified using systematic metal detector prospection (equipment by White's Electronics). The application of other destructive methods (microtrenching) for the verification of the most significant results will be considered by archaeologists according to the results of non-destructive investigative methods.
THE FIRST NEW RESULTS
The first year of the non-destructive
survey project (2003) brought some new and somewhat unexpected results.
Geophysical surveys of selected areas were conducted at four oppida
over a total surveyed area of approx. 8.5 ha (Křivánek 2004). The
wide-area magnetometric survey of the inner, meadow part (approx. 3.2 ha)
of the Nevězice oppidum identified various sub-surface situations:
concentrated anthropogenic activities (sunken settlement features and the
remains of shorter ditch enclosures), empty zones (possible lines of
communication) and geological changes in the bedrock (Figure 5). Another
magnetometric survey in the outer, wooded part (approx. 1.1 ha) of the
Závist oppidum (Figure 6) identified the sub-surface remains of 2
separate and previously unknown entrances (a possible gate and another
simple entrance; Křivánek 2003b) in the outer system of multiple ditch and
rampart fortification (Figure 7). Further, experimental magnetometric
prospection of another area at Závist known as 'Šance' (approx. 0.45 ha)
proved from the distinguished parallel lines of ploughing that this
recently wooded area was previously occupied by arable fields (since at
least 1780 forest is shown here even on the old maps of the first Austrian
military (Josephine) mapping - Figure 8).
RESEARCH TEAM Project lead investigator: Institute of Archaeology of
the Academy of Sciences of the Czech Republic RNDr. Roman Křivánek -
geophysicist (project leader)
PhDr. Petr Drda - archaeologist
ing.
Čeněk Čišecký- computer specialist
Project co-investigators: National
Museum, Prague
Mgr. Zuzana Karasová - archaeologist
PhDr. Pavel
Sankot - archaeologist
Mining Museum, Příbram
Mgr. Rostislav Korený
- archaeologist
No. of the project in the Grant Agency of the Academy
of the Sciences of the Czech republic: A8002301 (2003-2007)
References
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- BŘEŇ, J. 1975. Zvláštní typy sídlištních objektů na keltském oppidu v Třísově u Českého Krumlova (Special Types of Settlement Structures at the Celtic Oppidum of Třísov, District Český Krumlov, South Bohemia). Časopis Národního Muzea 144: 199-136.
- ČIŽMÁŘ, M. 1989. Pozdně laténské osídlení předhradí Závisti (Die spätlatènezeitliche Besiedlung der Vorburg von Závist.) Památky archeologické 80: 59-122.
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- JANSOVÁ, L. 1986 Hrazany. Keltské oppidum v Čechách, I (Hrazany. Das keltische Oppidum in Böhmen, Band I.) Prague: Institute of Archaeology.
- JANSOVÁ, L. 1988 Hrazany. Keltské oppidum v Čechách, II (Hrazany. Das keltische Oppidum in Böhmen, Band II.) Prague: Institute of Archaeology.
- JANSOVÁ, L. 1992. Hrazany. Keltské oppidum v Čechách, III (Hrazany. Das keltische Oppidum in Böhmen, Band I.) Prague: Institute of Archaeology.
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- KŘIVÁNEK, R. 2001b: Early Medieval hillfort Přistoupim - an example of role of large scale magnetometric prospection to the correct protection of archaeological monument, in Archaeological prospection - 4th International Conference on Archaeological Prospection, Vienna, Sept. 19th-23rd 2001: 135-137.
- KŘIVÁNEK, R. 2001c Přínos měření cesiovými magnetometry pro průzkum i výzkum archeologických lokalit v letech 1999-2000 (Contribution of caesium magnetometer measurements in prospection and research of archaeological sites in 1999-2000.) Ve službách archeologie III (In service to Archaeology III): 114-131 Brno.
- KŘIVÁNEK, R.. 2003a: Uplatnění geofyzikálních měření v projektu Sídelní prostor pravěkých Čech (Use of geophysical measurements in the project Settlement pattern of prehistoric Bohemia), in V. Hašek, R. Nekuda & J. Unger (eds) Ve službách archeologie IV (In service to Archaeology IV): 94-103. Brno.
- KŘIVÁNEK, R. 2003b: Contribution of geophysical measurements for survey and protection of hillforts, in. M.O. Altan (ed.) Proceedings of the XIXth International Symposium CIPA 2003, New Perspectives To Save Cultural Heritage, Antalya (Turkey) Sept. 30th - Oct. 4th 2003: 389-391 CIPA Istanbul: 389-391.
- KŘIVÁNEK, R. 2004. Geofyzikání průzkumy v archeologicky nezkoumaných částech českých oppid, zpráva o průběhu prací v roce 2003 (The geophysical surveys in archaeologically non-excavated areas of Czech oppida, 2003 report.) Archives of the Institute of Archaeology in Prague, ref. no. 352/04.
- MOTYKOVÁ, K., P. DRDA & A. RYBOVÁ. 1984. Opevnění pozdně halštatského a časně laténského hradiště Závist (Fortification of the Late Hallstatt and Early La Tène Stronghold of Závist.) Památky archeologické 75: 331-444.
- RYBOVÁ, A & P. DRDA. 1994: Stradonice. Rebirth of the Celtic oppidum. Prague: Institute of Archaeology.
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