Basic archaeological methods, analysis and interpretation

Disclaimer

The article below was originally written in the form of an undergraduate assignment for the Greek Open University in 2007, during a period when the author's academic skills were still under development. Although the quality of this article does not match the quality of later examples of the same author's work, it is written in a thorough manner and contains useful information to nowadays students and other readers with non-specialised knowledge; therefore, it has been proudly included on this website.

The reader needs to be warned that the original assignment, on which this article was based on, was written in Greek and was intended to be read by specialised academics. Despite the author's best intentions to present his essay in the clearest way possible, some points and arguments might still be lost in translation. The author recommends that for any unknown words or specialised vocabulary, the readers should refer to the web for additional information.

The author admits that the bibliography for this article is limited, matching the requirements of an undergraduate assignment of this level. The author did not include any additional bibliography during the translation of his work in English due to time and access limitations. It must also be noted that the original bibliography for this article was studied from translated copies in Greek; therefore, the page numbers suggested in the citations below match the page numbers of the translated copies and not the original volumes.

Introduction

This article introduces the non-specialist to the basic methods of archaeological research. The author focuses on specific aspects of archaeology according to his own interests. The paper is divided in five sections. The first section discusses the basic principles of archaeological research, the focus of various archaeological methods and the basic recording stages in archaeological fieldwork. The second section focuses on three methods for the recovery of archaeological data, which are aerial and satellite photography, land surveying and excavation. The third section focuses on the author’s favourite topic, which is sub-terrestrial investigations. The fourth section briefly discusses the classification methods employed in archaeology, as well as post-excavation analysis and interpretation. Emphasis is placed on dating, which is a separate field of laboratory-based archaeology. The final section summarises some key points from the previous discussions.

Basic steps of archaeological research

Before any archaeological investigation, the researchers structure the questions they wish to answer; they note the issues they wish to address and they formulate a plan for their work. The questions, which are set at the beginning of the investigation, do not necessarily bias the results. In fact, in modern archaeology it is quite common to re-evaluate the questions at different phases of the project; based on the archaeological data, the project is likely to be adjusted. Furthermore, the theories employed for the interpretation of archaeological data are likely to be abandoned, modified, adjusted or enriched with new questions. The whole process resembles a living organism, who is subject to dynamic changes: when new evidence is added, old evidence changes (Coucouzeli 2003, 112).

The basic steps of a standard archaeological investigation are seven: (1) the establishment of an investigation plan; (2) the preparation for the project’s execution; (3) the recovery of archaeological data; (4) the classification of archaeological data; (5) the analysis stage; (6) the interpretation stage; and (7) the publication of the final results. The largest variety of archaeological methods is usually employed for the recovery of archaeological data, which involves the collaboration between archaeologists and other scientists, such as geologists, environmentalists, biologists, chemists, mapping engineers, sociologists, ethnologists, etc. In that sense, an archaeological team is an interdisciplinary research team consisting of different professional specialisations (Coucouzeli 2003, 121-3).

Methods of recovery of archaeological data

The recovery of archaeological data takes place in three stages: (1) the location of the archaeological site, (2) the determination of its boundaries and (3) the excavation of the selected site. For the location and determination of an archaeological site, archaeologists initially survey a larger geographical area; they determine the nature of the broader site, its total size, its characteristic features and its possible function during the past. For the location and determination stages, archaeologists employ a variety of methods, which include aerospace mapping, surface (land) surveying and sub-surface investigation (Coucouzeli 2003, 121-3).

According to the authors view, aerospace mapping is perhaps the most useful surveying method, particularly from high altitudes. It includes aerial photography and telescopic scanning by aerial radars or satellites (1). Aerial photographs are used for the location and determination of an archaeological site, as well as for the preparation of an efficient and accurate surface scan, which is also know as land survey. In practice, aerial photographs determine the larger boundaries of an area of specific archaeological interest, within which the archaeologists can determine the presence of smaller archaeological sites or areas of specific archaeological interest. They provide information related to the overall size of an area, its geomorphology and its possible functions during the past. In relation to the latter, aerial photographs can reveal features of ancient landscape, such as roads, watering channels and ditches, crop-marks, filed boundaries, land terraces, etc. (Coucouzeli 2003, 126).

The photographs are taken from aeroplanes at different reception angles, depending on the objective. Diagonal photography offers better perspective and higher performance images. Vertical photography is more suitable for mapping and generating two-dimensional ground plans. Archaeological features present in three ways: (1) as ‘shaded’ lines (e.g. walls or ditches appear as dark-coloured linear patterns on the ground), which become easily detectable if the photographs are taken early in the morning or late in the afternoon; (2) as plots of land with traces of cultivation activity, detected by the density of vegetation above an archaeological feature; (3) as crop-marks on the soil, which has been cleared-out or ploughed in the past to form the boundaries of an archaeological position (e.g. a ditch or embankment surrounding a burial mound) (Renfrew C. & Bahn P., 2001, σ.80-83).

Modern technological developments in aerial photography contribute a lot more to archaeological investigations compared to the previous decades. During a photographic scan, camera operators can nowadays use infrared film (2), which captures reflected sunlight and colours it differently depending on the surface’s reflectivity, particularly in the case of ancient cereal crops. Another interesting application is the use of thermic cameras (thermography), which detects different soil temperatures. Thermography reveals cooler sub-terrestrial features, which might associate with ancient water channels or irrigation networks (Renfrew & Bahn 2001, 80-83).

Aerial radar scanning is conducted with SLAR devices mounted on aeroplanes and SIR or SAR devices mounted on spaceships. This technique is used to send microwave pulses to the ground, which reflect back to the scanner. The reflection’s duration time and the signal’s intensity are used to define the initial distance between the scanner and the examined area. Archaeological features are identified due to soil hardness or excessive humidity, which alter the radar’s signal intensity. The above techniques have major advantages as they can penetrate the atmosphere regardless of weather conditions and can penetrate the soil regardless of hardness or vegetation density. They provide useful information on surface and sub-surface changes in the archaeological landscape and they can also be used in underwater archaeology for the location of ancient shipwrecks (Coucouzeli 2003, 128).

Satellite radar scans record the intensity of infrared radiation, which is emitted in different wavelengths in relation to the surface’s condition. These wavelengths are recorded electronically and then converted to visual images, which are highly sophisticated. Satellite radar scanning has two major advantages: firstly, it can cover large geographical areas is short time, and secondly, its infrared images are not obstructed by dense vegetation. This enables the technique to reveal large yet invisible archaeological sites, often covered in dense jungle, such as the Mayan cities of the Yucatan Peninsula between Guatemala and Mexico. Of course, the technique has two major disadvantages: firstly, the images can often be inaccurate and dysfunctional due to their large scale, and secondly, image clarity is unsatisfactory as the scanning only picks up features ranging between 18m and 27m (Coucouzeli 2003, 129).

Land surveying, which usually follows aerospace mapping, is performed by ground teams. These teams of trained specialists are dispersed on large plots of land, which they field-walk according to specific methodologies related to the questions they wish to investigate. Before any land survey, the archaeologists need to establish six criteria: (1) whether the sector will be investigated by chronological or geographical criteria; (2) the surveys intensity degree, which can either be extensive or intensive; (3) the application of full-extent survey or the use of statistical sampling methods, which are significantly faster; (4) the determination of the ‘sampling units’, which can be rectangular grids or straight lines; (5) the statistical method used for the samplings, which can be random, systematic, stratified/random or stratified/systematic; and (6) the artefact collection strategy based on newer or older approaches. During land surveys, archaeologists come into first contact with the archaeological site and collect primary artefact data, which is visible on the surface (e.g. pottery, stone tools, building materials, etc.) (Coucouzeli 2003, 130-47).

Land surveying can be supplemented by sub-surface investigations, which belong to three major types: (1) geophysical methods, which include magnetic imaging scanning, electrical resistance scanning, ground penetration radar scanning and sonar scanning; (2) geochemical methods, which include phosphate analysis and trace element analysis; and (3) core drilling methods (Coucouzeli 2003, 130-47). Sub-surface investigations will be discussed in more detail in the following section of this article.

Excavation is the oldest and most widely known process for the collection of archaeological data. Unlike amateur excavations of previous centuries, modern archaeology is precise and based on a specific excavation methodology. It aims in obtaining the maximum amount of archaeological information with the minimum amount of destruction in the site. After all, a certain degree of destruction is expected to occur as archaeology is by definition a destructive science. Excavations are divided in two types: rescue and systematic. Both use two methods of digging an archaeological site: the vertical or stratified method and the horizontal or open-plan method. Other excavation methods consist of variations or combinations of the above two and are used in specific occasions. These are the quadrant method, the scaled section method and the ‘scraping’ method. An excavation is designed to investigate an area that has been covered by soil and the only way to access information is by digging. An excavation usually takes place slowly and careful, revealing the information hidden in each soil layer step by step. Before moving to the next soil layer, all information needs to be thoroughly recorded as there is no way to take the same step back. The recording of archaeological information on site includes an excavation log, numerous photographs of features and artefacts, as well as site plans, topographic and stratigraphic diagrams (Coucouzeli 2003, 147-59).

Geophysics and geochemistry: a little more on sub-terrestrial investigations

In the author’s own view, sub-terrestrial investigations require some additional discussion due to their scientific nature and interdisciplinary character. Such investigations allow archaeologists to locate and evaluate an archaeological site quickly and at low cost, without destroying the archaeology under its surface, at least not during the initial phases of investigation. Sub-terrestrial instigations do not stand on their own and are not performed randomly; instead, they follow aerial photography or satellite radar scanning and are simultaneously supplemented by land-surveying. Before conducting any form of sub-terrestrial investigation, the previous three methods are used to define the exact boundaries of the archaeological site under examination (Coucouzeli 2003, 141).

In comparison with any other method for the collection of archaeological data, sub-terrestrial investigations require extreme caution as there is no visual contact with the data. These require a different and intelligent way of thinking, additional planning, an ability to observe small details, and perhaps some imagination when the final image is not clear. The principle behind all geophysical methods is the penetration of the soil’s surface and the detection of sub-terrestrial anomalies attributed to human activity. Geophysical scans can be conducted with instruments measuring either the soil’s magnetic charge, electric resistance or sound refraction.

A magnetic scan, commonly referred as magnetometry of just mag, is conducted with two types of equipment: plain magnetometers and magnetic flux meters. Both instruments are dragged on the site’s surface, along predetermined parallel lines or paths. During the scan, the instruments detect sub-terrestrial concentrations of unusually large magnetic charges. Such magnetic charges are likely to indicate two types of information: (1) materials that have been purposely exposed to fire (e.g. ceramics, hearths, metallurgy debris, etc.); (2) decomposed organic materials associated with human habitation (e.g. discarded food remains). Magnetic flux meters show significant advantages compared to plain magnetometers as they are not affected by external interference, such as underground cables, wires, metal fences, etc. On the other hand, both instruments cannot penetrate depths exceeding 1m. If this is required, then archaeologists need to conduct a magnetic capacity scan, which combines a magnetic flux capacitor and various tube-shape drills. During this technique, the instrument records the sub-terrestrial magnetic capacity in different depths, which is then compared with the magnetic capacity of the surface layer (Coucouzeli 2003, 142-4).

Another method of geophysical investigation is electric resistance scanning, commonly referred as resistometry or just res. This method is similar to magnetic scanning, although instead of measuring magnetic charges, it measures the fluctuations of electric charges. More specifically, electrodes are used to send electric charges into the soil, which are altered by its density. The fluctuations of the soil’s resistance in each electric charge are then picked up by the device. Although this method is not affected by the presence of objects in the sub-surface, it is particularly sensitive to weather conditions (Coucouzeli 2003, 142-4).

The basic principles of both methods are combined together in surface interface radar scanning (SIR), which detects electric and magnetic anomalies at the same time. Surface interface radars or ground penetration radars transmit and receive electromagnetic signals or radio waves, measuring their distortion. Such devices are particularly useful as they can accurately measure the depth of specific objects, offering clear images of transverse sections. These provide stratigraphic information by the identification of numerous material buried under the soil. Ground penetration radars have two major disadvantages: they are highly sensitive to weather conditions and their operation is complicated (Coucouzeli 2003, 142-4).

Sonar scans are primarily used in maritime archaeology. During this technique, a sonar device mounted on a boat transmits sonic pulses, which are then reflected back to the device. The device captures the reflected signal and measures its distortion, which is due to the mechanical properties of the seabed reflecting the sonic pulse (Coucouzeli 2003, 142-4).

Geochemical methods for sub-terrestrial investigations are based on the identification of specific chemical elements into the soil. A cylindrical sample, which is drilled out of the topsoil layer, is subject to chemical analysis, which is likely to reveal phosphate salts, copper or lead trace elements. Phosphate salt analysis offers information in relation to the habitation extent of a certain area. Phosphate salts are produced after the decomposition of organic debris associated with human activities (e.g. garbage, animal bone remains, dung, etc.). A major problem with this technique is that phosphate salts are likely to vanish along the years due to the nature of the soil. Metal trace element analysis is similar to phosphate salt analysis, only targeting inorganic human debris. Copper or lead trace elements associate with metallurgy and their discovery is likely to point towards industrial activities or ancient workshop practice (Coucouzeli 2003, 144-7).

Sub-terrestrial investigations are also performed with drilling techniques. Such techniques use drilling rigs or metal rods, which penetrate the soil in greater depth than the previously discussed methods. They provide information about soil cohesion and the peripheral stratification of buried remains. In soil drilling, a small hole is initially created into the soil. A tube, which is equipped with a surveillance device (e.g. periscope, photographic camera, television camera, etc.), is inserted into the hole in order to record the subsoil’s stratification. Drilling is less destructive compared to excavation, especially for underground structures of fragile artefacts; however, information is significantly limited (Coucouzeli 2003, 144-7).

Methods of classification, analysis and interpretation of archaeological data

Classification, analysis and interpretation follow the recovery of archaeological data and are usually performed off-site. Their methods, which often take place in archaeological laboratories, supplement the research projects and advance them to publication level.

Classification methods are primarily used on artefacts. Archaeological artefacts are arranged according to their characteristic features, which are then combined with the context information obtained during their recovery. Through classification, artefacts offer useful information on human activities and the life of specific cultural groups in the past. Classifications relate to morphological, stylistic and technological characteristics of artefacts, or in other occasions they relate to their chronological, functional and cultural characteristics. Typologies are created according to the mutual characteristics among different artefact groups (Sbonias 2003, 184-7).

The analysis and interpretation of archaeological data can either focus on excavated artefacts or the broader archaeological area and its excavated features. The analysis is likely to focus on five aspects: (1) The study of settlement features and their spatial distribution. Such analysis targets the broader habitation area and produces geometrical distribution charts for the study of settlement patterns. Settlement patterns can be random, arranged in groups, widely spread, normal, hierarchical or centrally organised. (2) The study of natural environment through the analysis of ecofacts, which is the focus of environmental archaeology. Studies on geomorphology, palaeoeconomy, floral and faunal studies, as well as studies on climate change assist in reconstrcuctiong palaeoenvironment. (3) The study of social organisation, which explores spatial distribution patterns, mortuary data and the social role of gender. (4) The study of economic organisation, which explores the ecological and socio-political parameters of ancient economy. Ecological studies focus on the broader ‘economy of human survival’, which investigates human diet based on zoo-archaeological and palaeobotanic data, natural resources, natural supply and exploitation areas. In sociopolitical studies, economic activities are studied as part of a sociopolitical system, which includes the distribution of goods, exchange, commerce and workshop production. (5) The study of cognitive and symbolic structures, which focuses on the gradual development of human cognition and the symbolic aspects of human thought during the past. The later includes the study of cosmology, religion, ideology, pictorial symbolism in art, material culture with symbolic interpretation, etc. (Sbonias 2003, 193-236).

The analysis of archaeological data includes a variety of dating methods, offering relative or absolute chronologies. Relative chronology methods are further sub-divided into two groups: the archaeological methods of relative chronology (stratigraphy, typology, seriation) and the natural science methods of relative chronology (palaeoclimatology, fauna and flora analysis). In a similar manner, absolute chronology methods are further sub-divided into two groups: the historical methods of absolute chronology, which are based on recorded calendars, and the scientific methods of absolute chronology, which are based on physics and chemistry. The second sub-category includes some fascinating methods, such as radiocarbon dating (C-14), dendrochronology, potassium/argon dating (K-Ar), uranium/thorium dating (U-Th), and thermoluminescence dating. The above methods can be combined and offer chronological information reaching up to 4.5 million years before present. Furthermore, scientific dating methods can be used to cross-reference the chronology of all other types of archaeological finds (organic, inorganic, environmental, geophysical, etc.) (Coucouzeli 2003, 166-74).

Summary

Archaeological research includes a wide variety of analysis and interpretation methods, which can take place inside and outside the archaeological field. Modern archaeology usually requires the collaboration of a large interdisciplinary research team. The research questions and the conclusions produced by this team are constantly re-evaluated under the light of new evidence; therefore, no conclusion should be considered absolute and final (3).

Aerospace mapping offers detailed information on the location and identification of archaeological sites, followed by land surveying and sub-terrestrial investigations. The latter assists in deciding whether a site should be excavated; if so, excavation is the primary method for the collection of archaeological data. After the excavation, there is the classification, analysis and interpretation of archaeological data. Different methodologies are used for different types of archaeological finds (e.g. artefacts, ecofacts, etc.). These are supplemented by relative or absolute dating methods, which define the data’s chronological context.

Bibliography

Coucouzeli, A., 2003, ‘Methods for the recovery and dating archaeological testimonies’, in Papagianopoulou, A. (ed.) Archaeology in Greece, Volume I, The Historical Course of Archaeology, Definition, Focus, Basic Principles, Discipline Branches and Reflections, Patra: Greek Open University, 121-80.
Renfrew, C. and Bahn, P. (eds.), 2001, Archaeology: Theories, Methods and Practice, translated by Lilian Karali, Athens: Kardamitsas.
Sbonias, K., 2003, ‘Methods of classification, analysis and interpretation of archaeological testimonies’, in Papagianopoulou, A. (ed.) Archaeology in Greece, Volume I, The Historical Course of Archaeology, Definition, Focus, Basic Principles, Discipline Branches and Reflections, Patra: Greek Open University, 181-240.

Notes

1. When the paper was originally written in 2007, this used to be the case. In more recent years, however, the use of drones has become the main tool for aerial investigations as it is cheap, accurate and can focus on specific parts of an investigated area. It is particularly popular in commercial archaeology and is also being used for post-excavation mapping.
2. This is another anachronistic statement, as the original 2007 paper was based on bibliography from the early 2000s. Back then, the latest developments in digital photography had not been introduced into archaeology.
3. Not everybody will agree on this point. A further discussion on this statement requires some knowledge on archaeological theory and the differences between processualism and post-processualism. Further reading is advised.