Basic archaeological methods, analysis and interpretation

Disclaimer

The article below was originally written as an undergraduate assignment for the Greek Open University in 2007, during a period when the author’s academic skills were still developing. Although the quality of this article does not match that of later examples of the same author’s work, it is written in a thorough manner and contains useful information for 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, 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 readers consult the web for additional information on any unfamiliar words or specialised vocabulary.

The author admits that the bibliography for this article is limited, as required for an undergraduate assignment of this level. The author did not include any additional bibliography during the translation of his work into 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 that interest him. The paper is divided into 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 recovering archaeological data: aerial and satellite photography, land surveying, and excavation. The third section focuses on the author’s favourite topic: subterranean 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, note the issues they wish to address, and formulate a plan for their work. The questions 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 to interpret archaeological data are likely to be abandoned, modified, adjusted, or enriched with new questions. The whole process resembles a living organism, subject to dynamic change: 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 to recover archaeological data, which involves collaboration among archaeologists and other scientists, such as geologists, environmentalists, biologists, mapping engineers, sociologists, and ethnologists. 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. To locate and identify an archaeological site, archaeologists initially survey a larger area; they determine the nature of the broader site, its total size, its characteristic features, and its possible past function. For the location and determination stages, archaeologists employ a variety of methods, including aerial mapping, surface (land) surveying, and subsurface investigation (Coucouzeli 2003, 121-3).

According to the author's view, aerospace mapping is perhaps the most useful surveying method, particularly from high altitudes. It includes aerial photography and radar or satellite telescopic scanning (1). Aerial photographs are used to locate and determine an archaeological site, as well as to prepare an efficient and accurate surface scan, also known as a land survey. In practice, aerial photographs delineate the larger boundaries of an area of specific archaeological interest, within which archaeologists can identify smaller archaeological sites or areas of specific archaeological interest. They provide information on the overall size of an area, its geomorphology, and its possible past functions. In relation to the latter, aerial photographs can reveal features of ancient landscape, such as roads, watering channels and ditches, crop-marks, field boundaries, land terraces, etc. (Coucouzeli 2003, 126).

The photographs are taken from aeroplanes at different reception angles, depending on the objective. Diagonal photography offers a 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 have contributed much more to archaeological investigations than in 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 for ancient cereal crops. Another interesting application is the use of thermal cameras (thermography), which detect differences in soil temperature. Thermography reveals cooler subterranean features that might be associated 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 uses microwave pulses sent to the ground, which are reflected 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: they can penetrate the atmosphere regardless of weather conditions and the soil regardless of hardness or vegetation density. They provide useful information on surface and sub-surface changes in the archaeological landscape and can also be used in underwater archaeology to locate ancient shipwrecks (Coucouzeli 2003, 128).

Satellite radar scans measure the intensity of infrared radiation emitted at different wavelengths, which depend on the surface’s condition. These wavelengths are recorded electronically and then converted into highly sophisticated visual images. Satellite radar scanning has two major advantages: first, it can cover large areas quickly, and second, its infrared images are not obscured 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 scanner only picks up features ranging from 18m to 27m (Coucouzeli 2003, 129).

Land surveying, which usually follows aerospace mapping, is performed by ground teams. These teams of trained specialists are dispersed across large plots of land, which they field-walk using specific methodologies tailored 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 first come into contact with the archaeological site and collect primary artefact data 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 method for collecting archaeological data. Unlike amateur excavations of previous centuries, modern archaeology is precise and follows a specific methodology. It aims to obtain the maximum amount of archaeological information with the least possible destruction at the site. After all, a certain degree of destruction is expected, as archaeology is, by definition, a destructive science. Excavations are divided into 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 on specific occasions. These are the quadrant method, the scaled-section method, and the ‘scraping’ method. An excavation is designed to investigate an area covered by soil, and the only way to access information is by digging. An excavation usually proceeds slowly and carefully, revealing the information hidden in each soil layer as it is uncovered. 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, site plans, and topographic and stratigraphic diagrams (Coucouzeli 2003, 147-59).

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

In the author’s view, subterranean investigations warrant 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 subterranean investigation, the previous three methods are used to define the exact boundaries of the archaeological site under examination (Coucouzeli 2003, 141).

Compared with other methods for collecting archaeological data, subterranean investigations require extreme caution, as there is no visual contact with the data. These require a different, intelligent way of thinking, additional planning, the ability to observe small details, and perhaps some imagination when the final image is unclear. 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 using instruments that measure soil magnetic charge, electrical resistance, or sound refraction.

A magnetic scan, commonly referred to as magnetometry or 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, metallurgical debris, etc.); (2) decomposed organic materials associated with human habitation (e.g. discarded food remains). Magnetic flux meters offer significant advantages over plain magnetometers, as they are not affected by external interference, such as underground cables, wires, or metal fences. On the other hand, neither instrument can 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-shaped drills. During this technique, the instrument records the subterranean magnetic field at different depths, which is then compared with the magnetic field of the surface layer (Coucouzeli 2003, 142-4).

Another method of geophysical investigation is electric resistance scanning, commonly referred to as resistometry or just res. This method is similar to magnetic scanning, but instead of measuring magnetic charges, it measures fluctuations in electric charges. More specifically, electrodes are used to send electric charges into the soil, which are altered by its density. The device then detects fluctuations in the soil’s resistance during each electric charge. 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 in surface interface radar scanning (SIR), which simultaneously detects electric and magnetic anomalies. Surface interface radars or ground-penetration radars transmit and receive electromagnetic signals, or radio waves, and measure 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 identifying numerous materials buried beneath the soil. Ground-penetrating radars have two major disadvantages: they are highly sensitive to weather conditions and their operation is complex (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 in the soil. A cylindrical sample drilled from the topsoil layer is subject to chemical analysis, which is likely to reveal phosphate salts, trace amounts of copper, or lead. Phosphate-salt analysis provides information on the extent of habitation in a given 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 leach over time due to soil conditions. 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).

Subterranean investigations are also conducted using drilling techniques. Such techniques use drilling rigs or metal rods that penetrate the soil to greater depths than those achieved by 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 in 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 than excavation, especially for underground structures containing 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 provide useful information about past human activities and the lives of specific cultural groups. Classifications relate to the morphological, stylistic and technological characteristics of artefacts, or, on other occasions, to their chronological, functional and cultural characteristics. Typologies are created on the basis of the mutual characteristics of different artefact groups (Sbonias 2003, 184-7).

The analysis and interpretation of archaeological data can focus either on excavated artefacts or on 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 the natural environment through the analysis of ecofacts, which is the focus of environmental archaeology. Studies on geomorphology, palaeoeconomy, floral and faunal diversity, and climate change help reconstruct the 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 the ancient economy. Ecological studies focus on the broader ‘economy of human survival’, which investigates human diet based on zooarchaeological and palaeobotanical data, natural resources, and areas of natural supply and exploitation. 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 latter 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 that provide relative or absolute chronologies. Relative chronology methods are further subdivided into two groups: archaeological methods (stratigraphy, typology, seriation) and natural science methods (palaeoclimatology, analysis of fauna and flora). In a similar manner, absolute chronology methods are further subdivided into two groups: historical methods, which rely on recorded calendars, and scientific methods, which rely on physics and chemistry. The second subcategory 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 to provide chronological information extending back 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 analytical and interpretive methods that can be carried out both within and outside the archaeological field. Modern archaeology usually requires the collaboration of a large interdisciplinary research team. The research questions and conclusions produced by this team are continually re-evaluated in light of new evidence; therefore, no conclusion should be considered absolute or 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 collecting 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). 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 was the case. In recent years, however, drones have become the primary tool for aerial investigations, as they are cheap, accurate, and can focus on specific areas. 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 a 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 of archaeological theory and the differences between processualism and post-processualism. Further reading is advised.