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.

Sometimes archaeological sites are found accidentally, but when archaeologists find them, they are usually found due to a purposeful investigation of a specific region. The attempt to document a human presence on a landscape is called “survey archaeology,” and in the process, archaeologists are looking for both isolated finds (a piece of jewelry that fell off while someone was walking, an arrowhead that fell to the ground during a failed hunting attempt, or a single bottle discarded by a weary traveler, for instance) and sites, locations where numerous artifacts and/or features can be found. Sites can range from locations that were short lived (a hunting site that was used for a few hours while deer were being processed, for example) to sites that were inhabited as a densely inhabited village for centuries.

Archaeological surveys are used to identify potential sites, locate artifacts, and provide the raw data for more complex interpretations. For example, finding similar artifacts across a large geographic area can help us to figure out what ancient trade networks might have been used, how ancient economies functioned, or how people were using lands. Traditional surveys, more commonly known as pedestrian surveys, require physical presence at a location and specific techniques in looking for artifacts on the surface of the ground. These surveys are vital to the entire process of site identification and excavation. However, surveys alone are not sufficient to get an idea of what might be present. Instead, archaeologists have long relied on mapping of these individual artifacts to determine the extent of the site . Modern technology has allowed for the integration of survey data into larger archaeological workflows, giving us much greater speed, precision, and accuracy even when full excavations are not possible or the extent of an archaeological site is not know.

Geographic Information Science (GIS) is not a single method, concept, or program. Instead it is a way of organizing, displaying, and analyzing data that has some type of geospatial component. This interdisciplinary science has been applied to fields from ethnography to urban planning, wildlife management to mining, and economics to anthropology, among others. In today’s world, GIS is intimately tied with Remote Sensing (RS), a method of collecting data without being physically present at a location.

Sites not uncovered by chance or by reviewing archaeological and historical documents are usually detected using three type of reconnaissance: ground survey, subsurface detection and aerial reconnaissance. These types of reconnaissance do not typically involve excavation and instead examine what is visible – whether it is accessible on the surface or noted in subsurface patterns.

Ground Survey

Historically, the most common way to find sites has been through 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.

Pedestrian surveys are a cornerstone of archaeology. These surveys rely on large teams of archaeologists and volunteers to walk a site in a specific pattern. Archaeologists line up and head in a specific direction. Their distance from each other will depend upon the landscape and how difficult or easy it may be to see artifacts and features. Sometimes material remains will be rather easy to see (a standing structure or bright blue piece of ceramic, for example), but other times they will be visible only by the trained eye. In dusty areas, artifacts will often take on the same color as the surrounding sediments, so archaeologists will need to know which shapes to look for in a monochromatic environment. In areas with lots of vegetation, you may need to train your eyes to look within and between the plants. You might not see the building materials of ancient structures, but their presence might be visible through mounds or depressions. Sometimes features will be identifiable only through changes in the vegetation. For example, plants trying to grow above the compact ground surface of an old, buried roadway will struggle to grow as well as other plants around them. Conversely, deeper soil accumulated within an old ditch or cellar will result in taller, healthier plants. You must keep an eye out for artifacts, structures, and suggestions that such items might be hiding underground.

When someone sees something, they alert their colleagues. The movement forward pauses so all team members can search that specific area. If only one item was found, they document it as an isolated find and use GPS to record the item’s location. Then, depending upon local laws, whether or not the artifact is in danger of being destroyed if left in place, and the methods used in that specific project, archaeologists will either collect the item (in a bag with the location of the find clearly written out) or return it to its original location.

If they have found a site, they map out the extent of the feature and artifact spread and determine whether or not any of the artifacts they have found should be collected. In some projects, all artifacts are mapped in place, photographed, and then left in place. At other times, especially when a site is in danger of being destroyed or when the collection of artifacts will help archaeologists answer specific questions, artifacts will be mapped and photographed while in place and then collected. Sometimes all artifacts are collected from the surface, but oftentimes only some artifacts will be collected to serve as a sample of what is present at the site.

Anytime something is found, the team will pause while the item is examined, GPS coordinates are taken, and the item is “tagged and bagged ”. This involves completing a standardized form that includes information like the date, GPS coordinates, individual who identified the object, and any contextual information that may be relevant (see these forms from the University of Arkansas).

When the goal of a project is to find a specific type of site, survey may end when that type of site is found. However, when the goal of a project is to determine how many different sites exist on a landscape, the survey will continue after each site has been mapped in and documented.

Subsurface Detection

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.

By recording how long it takes for the radar signal to hit something and return to the machine, the readings are then manipulated with a computer. The results can tell the archaeologists whether or not any large features (like wells, houses, or roads) have impacted the sediments beneath the ground surface because those features will provide a different pattern than the surrounding, undisturbed sediments.

Other passive geophysical sensing devices can measure physical properties of the soil, such as gravity and magnetism. 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.

Aerial Reconnaissance

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.

Archaeologists are able to use a wide variety of technologies to practice aerial survey. We can use our eyes during flights and can use photographs and videos taken from cameras attached to kites, balloons, drones, and planes. When conducting aerial survey, we are looking for visible structures as well as features that look out of place (such as circular mounds, lines or ridges, and depressions) and unusual vegetation growth, each of which might suggest there are features underground.

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 you have just seen, archaeologists can use aerial images to help us find and document archaeological sites. These images can be captured via drones, satellites, and aircraft equipped with a variety of laser technologies. Sometimes archaeologists collect their own data, but they can also use images already collected and accessible through Google Earth. Archaeologists who rely heavily or mostly upon satellite and infrared imagery (images from space) to find sites are affectionately called “space archaeologists.”

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.

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.

Want to learn more? Some of the biggest breakthroughs in modern archaeology are happening thanks to LIDAR. If you want to learn more about this and happen to have Disney+, you might enjoy the following two shows that focus on using LIDAR to expand our knowledge of the ancient world: “Lost Cities with Albert Lin” and “Lost Treasures of the Maya.”

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.

Note: Parts of this chapter were written by author Ian S. Ray in a beta version of Traces.

Part of this chapter is from Traces by Whatcom Community College and is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License, except where otherwise noted.

Parts of this chapter are shared under a CC BY-NC license and were originally authored, remixed, and/or curated by Amanda Wolcott Paskey and AnnMarie Beasley Cisneros (ASCCC Open Educational Resources Initiative (OERI)) .