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6.1: Introduction to Finding Archaeological Sites

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    It may seem like archaeologists just walk into the field and begin digging (and discovering amazing artifacts)! If only that were true. Actually, extensive planning is required before tools ever strike the ground. Before excavation or even a survey can begin, the archaeologists must formulate a research question, which will guide all aspects of the work—where to excavate, what kinds of data to collect, and what types of artifacts are relevant. This critical step never gets portrayed in the media.

    Once the core research question has been proposed and the project parameters have been designed, the next task is to locate the specific study site. Of course, not all archaeological data and sites are “lost.” Many are well known, such as the Great Wall of China and the Pyramids in Egypt. But how are sites located when they have been “lost” to time? Sometimes, sites are uncovered by chance. The Terra Cotta Army in China, for example, was discovered by a farmer who was digging a well and was surprised to find a ceramic head in his bucket! Another way to identify archaeological sites is by investigating previous studies by reviewing cultural resource management (CRM) reports, ethnographies, and historical accounts. Works of literature have been useful as well. Homer’s The Iliad spurred discovery of the ancient city of Troy by archaeologists who based their search on the geographical description of the city in the text.

    Sites not uncovered by chance or by reviewing archaeological and historical documents are usually detected using three type of reconnaissance: aerial reconnaissance, ground reconnaissance, and subsurface detection.

    As the name suggests, aerial reconnaissance methods find, record, interpret, and monitor archaeological sites from above. Aerial photography was first used in archaeology in the early twentieth century and its use expanded significantly after World War I. Archaeologists and their pilots would fly over areas they were interested in investigating, looking for signs of archaeological sites and land formations in which sites or artifacts are commonly found and then photographing them from the air. Aerial reconnaissance is particularly useful when studying large-scale patterns of habitation and use of a landscape. The photos also sometimes reveal buried sites in a surprising way. Earth works, crop marks, and soil marks, which are all evidence of human habitation and cultivation, are often apparent in aerial photographs, and trained eyes can identify areas in the images that suggest archaeological remains beneath the surface. For example, earth works, which consist of buried ditches, banks, and stone walls, often show up as shadows in aerial photos. Crop marks, on the other hand, appear in vegetated areas when plants are growing over buried walls or ditches that stunt or boost their growth relative to the rest of the plants in the area. Soil marks can be revealed when, for example, a plow uncovers a buried stone feature that is close to the surface, exposing a distinct difference in soil color and texture.

    As technologies have changed and developed, new avenues of aerial reconnaissance have opened up. One such technology is Light Detection and Ranging, known as LiDAR, which involves lasers scanning landscapes and sites from an aircraft to create digital elevation models. This technology “sees through” dense vegetation and groundcover found in tropical jungles, allowing archaeologists to identify overgrown structures. Recent applications of LiDAR in Mesoamerica have been incredibly successful, leading to the discovery of 60,000 Mayan structures that include homes, fortifications, and causeways. Thanks to this work, we now know that the Mayan world was much more densely populated and interconnected than previously thought. Archaeologists have revised their estimates of the Mayan population to include millions more people in previously unknown city-states.

    The availability of drones with photographic equipment attached has dramatically increased the accessibility and affordability of aerial reconnaissance efforts. Archaeologists who once needed to hire a pilot can conduct many aerial reconnaissance flights themselves.

    With the advent of Google Earth, initial reconnaissance flights might not be needed since Google’s satellite imagery is freely available and can often provide necessary aerial images. Since this tool is right at a person’s fingertips, it can be used as a first pass of preliminary reconnaissance, guiding future, more-detailed inquiries with techniques that offer greater resolution. Google Earth also provides historical data through satellite imagery archived over time, allowing archaeologists to compare views of a location, potentially revealing changes in environmental conditions, water levels, and even a site’s condition (before plowing, construction, or some other disturbance).

    Since Google Earth is free and drone technology is increasingly affordable, barriers to conducting reconnaissance have decreased, which is good for archaeologists but also allows anyone who is curious to search. Many sites had been protected from disturbance and looting by the fact that they were buried underground or overgrown by the jungle—few people knew they were there. Now, as drone technologies and Google Earth satellite imagery make the search accessible to everyone, sites are being discovered, disturbed, and looted, a sad drawback of these scientifically useful modern technologies.

    Eventually, of course, archaeologists must get out of airplanes and their offices and check out potential sites in person to see what is actually there. They conduct ground reconnaissance to find, record, interpret, and monitor archaeological sites. This type of reconnaissance does not involve excavation. It examines what is visible and accessible directly on the surface of the ground. A primary tool is a ground survey—a systematic search for artifacts by methodically walking the site. How the survey is conducted depends on one’s research question and the specific conditions at a site. Researchers can, for example, consider an area outlined by a trajectory such as a radius or a line extending outward from a central or starting point. The surveyors look for artifact scatter and/or unusual discolorations that suggest prior human behavior. When a possible artifact or feature is identified, the surveyor places a flag in the ground to identify its location and continues surveying. No excavation occurs at this time. Once the survey is complete, the flagged locations are precisely identified by GPS coordinates. Their locations are recorded and artifacts can then be collected, if appropriate, given the research question.

    Archaeologists also have subsurface detection tools that allow them to conduct reconnaissance below the surface of the ground without excavating. Important nondestructive tools are geophysical sensing devices such as Ground Penetrating Radar (GPR). These devices actively probe underground by passing various types of energy, laser, or radio waves through the soil and measuring how the waves are reflected back to find out what is below the surface. Passive geophysical sensing devices measure physical properties of the soil, such as gravity and magnetism. As with LiDAR, these tools capture data that generate a map of what lies below the surface. These highly technical nondestructive subsurface methods require a trained practitioner capable of running the machines over the site and interpreting the resulting data.

    As a last resort, archaeologists can use probes that physically dig below the surface to learn more about what lies underground but risk damaging the site. A probe involves using a rod or auger, which looks like a giant drill bit, inserted into the ground to drill down as far as possible into the soil. The auger is then brought back to the surface, carrying with it samples of soil (that may or may not contain artifacts) from various levels below the surface. It is easy to see why this method must be used sparingly and with caution as it involves plunging a sharp, destructive device into the ground, potentially damaging anything it encounters, including human burials. Another method of physically examining the subsurface is making shovel test pits, which are essentially very small excavations, usually one meter by one meter in size (it varies), to see if there is a potential archaeological site under the surface. Typically, several test pits are opened at the same time at a consistent distance from one another. This method is particularly useful for confirming the results of other forms of reconnaissance.

    Terms You Should Know

    • aerial reconnaissance
    • auger
    • crop marks
    • earth works
    • Ground Penetrating Radar (GPR)
    • ground reconnaissance
    • Light Detection and Ranging (LiDAR)
    • probe
    • shovel test pits
    • soil marks
    • subsurface detection
    • survey

    Study Questions

    1. Research an existing site at which earth works, crop marks, or soil marks were found. What was visible aerially? What was determined about the site through further investigation?
    2. Why would an archaeologist strive to limit the use of probes such as augers and test pits?
    3. Compare and contrast aerial and ground reconnaissance strategies. What are some benefits and pitfalls of each?
    4. Describe how new technologies such as drones, GPS, and Google Earth are changing how archaeologists locate sites.
    5. What are some potential benefits and drawbacks of the new technologies being applied to archaeology today?