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Field-walking

Field-walking, otherwise known as surface collection, is a non-intrusive archaeological method that can serve multiple purposes prior to excavation. It is the process of traversing an archaeological site and collecting visible deposits in recently ploughed topsoil, and contributes to the mapping of acquired materials in order to identify the topographical and chronological characteristics of a site prior to excavation . Fieldwalking can be conducted systematically or unsystematically. The former is a more subjective technique as it involves scanning the ground along a field-walker’s path for artefacts to be located and recorded. The latter involved a grid system whereby the survey area is divided into a grid of equally-sized squares that are then traversed systematically.

Materials

The materials typically collected in fieldwalking consist of pottery, flint, and ceramic building material (CBM), but may also include minerals and organic material depending on the project objective. Moreover, the successful detection and recovery of these drastically depend on the impacts of natural, geological, and cultural processes. Weather and soil types must be considered before practising surface collection - dull weather is ideal in order to avoid shadow, and the best soil to field-walk should be moderately dry and not too affected by episodes of weathering and topsoil deterioration.

Ideal conditions

Surface collection is also best employed when the same sampling techniques are utilised throughout the survey. Approaches in technique as well as the field-walkers’ familiarity with the artefacts should be identical and maintained throughout in order to minimise the effects of random and systematic error in the dataset and enable fair comparisons of collected data across the site.

Methods

The key ideas behind the following methods are extracted from the works of Glenn Foard in the 1978 article "Systematic Fieldwalking and the Investigation of Saxon Settlement in Northamptonshire".

Density surface plan

This method involves traversing and recording deposits across the entire site, ensuring a complete understanding of the area. This census approach to survey is not typically practised because it can be time-consuming and in some cases can be subject to wild approximations when locating artefacts onto a map.

Random

The simplest and most flexible method of field-walking is the random sample, where field walkers are tasked to traverse the site with little guidance on direction. This method carries many uncertainties, namely because its subjectivity risks the under-representation of certain areas in the field. The likelihood of producing a skewed data set increases when the employment of landscape prospection is influenced by convenience and efficiency. These biases can be limited by adopting one of the following approaches.

Grid

Field-walkers systematically traverse the squares within a grid outline of the field. This is an adaptation to the census approach that ensures total coverage of the site and every single archaeological deposit, as well as its approximate position. The mapping of deposits are limited to the size and location of the square, meaning that less uncertainties are introduced in the formation of a deposit dataset.

Systematic traversing

A technique whereby the field is divided into equally spaced and parallel traverses for field-walkers to investigate. The entire site is not represented, but imbalances in the representation of deposits at the site are minimised. Especially when the traverses are numerous, subdivided, and evenly spread across the area, an efficient and reasonably precise extraction of distributional information from the site is ensured.

Case Studies

Assessing production and trade in central Italy during the Roman period

An amphora workshop Montelabate in Umbria, Italy, was in use from the mid-first to the fifth century AD. It is a key case study for the economy of production in the Umbrian Basin, and also for the practice of field-walking on multiple occasions.

Survey collection was first conducted at the site in 2010 as part of the Montelabate Project, which uncovered a key production area within walking distance of a rich clay deposit. This archaeological method formed the primary basis for scientific analysis of sampled clay beds, incorporating methods such as X-ray diffraction (XRD), and scanning electron microscopy (SEM), thermogravimetry (TG). The recovery of flat-bottomed wine amphora fragments during the collection survey at Montelabate in 2010, combined with chemical analysis, evidenced agricultural exploitation and the production of wine in the Montelabate valleys.

In 2012, the Universities of Cambridge and Queen’s Belfast directed the Montelabate Project under Dr Simon Stoddart (University of Cambridge), Prof. Caroline Malone (Queen’s Belfast). In the five-week excavation, a field-walking assessment accompanied by geophysical survey was employed once more to assess the distribution of surface materials at the summit of the hill. The finds revealed three Roman pottery kilns, insinuating productive amphorae production and intensive cultivation of vines in the landscape to support the workshop. This land occupation model was supported by collection surveys at the site earlier in 2010, whereby farm foundations of varying sizes, orientation, and periods of occupation at Montelabate were discovered. These farmhouses would have been integral to the nature of the workforce, accommodating free labourers moving around to meet the seasonal needs of agriculture.

*Please find relevant article for more images

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Domestic remains in the site of Aiali, Italy

In 2004 the Department of Archaeology and History of Arts at the University of Siena conducted field-walking and surface collection at Aiali. The site was occupied from the Roman to Mediaeval times and contained architectural structures of varying complexity. These ranged from large building complexes with courtyards and numerous rooms to residential/domestic buildings that lacked monumental features. The structural boundaries of the settlement were identified through the use of collection survey via the grid system method, which enabled the detection and analysis of high densities of artefact scatters. A grid system of 10x10m polygons contained the respective location of finds, which were planned into GIS and then exported to the Differential Geographic Positioning System (DGPS) in order to allow satellite navigation into the field and precise topographic localisation of deposits. Not only was collection survey important in securing the location of finds, it was also a useful way of confirming the success of using digital archaeological survey methods: “ground survey and the study of the collected material has confirmed the archaeological character and interpretation of the site as seen in the air, demonstrating a good level of correspondence between the aerial evidence and concentrations of archaeological finds”. Therefore, it is important to employ surface collection in the context of a multi-methodological approach to not only acquire information from a site directly but also to ensure the reliability and reproducibility of data extracted from other archaeological methods.

An example of African Red Slip Ware “A” (ARS).

After the typological organisation and quantification of collected ceramic data from the topsoil, the department was able to reconstruct developments in the site during the early and mid-imperial periods. Two key categories of pottery within the typology are defined as Black Glaze Ware (BGW), terra sigillata italica, and African Red Slip Ware “A” (ARS). Significant concentrations of ARS fragments in the archaeological site dating between the 2nd and mid-3rd centuries served as evidence for a major period of change and development in the site . This instance of collection survey then promoted further investigation into the social, economic, and political dynamics that informed such a trajectory.

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Map of Rail Baltica

Rescue archaeology: the Rail Baltic Project

The Rail Baltica (RB) project, a 240 km long railway route stretching from Tallinn through to Riga, Kaunas, and beyond into Central and Western Europe.

Fieldwalking was conducted on a segment of this route (from Tallinn to Ikla) as part of the execution of rescue archaeology in 2013 by the University of Tartu. Archaeological investigation prior to the construction of the railway was conducted over multiple stages. The recovery of Baltic history, particularly that belonging to Estonia and Latvia, was achieved via a series of archaeological methods, namely survey, field-walking and metal detection.

The initial stage of rescue archaeology entailed the location of potential sites along the track by analysing old and new maps for topographic anomalies (i.e. areas of black soil or cultivated fields suggesting the presence of an earlier settlement, the remains of buildings that no longer exist). These informed approaches to collection survey (stage two) by pinpointing areas of archaeological focus beforehand. A pre-existing knowledge of the size and condition of archaeological sites also enabled archaeologists to estimate the intensity of excavation and field-walking they necessitate. In this case study, field-walking was also conducted to detect new sites, which was also aided further by the use of metal detection. Metal detectors were mainly employed in this Project to uncover evidence for human settlement and activity below the topsoil, and from there establish periods of occupation (i.e. modern, mediaeval, prehistoric) within historical locations. The third and final stage was largely characterised by the excavation of sites. A key discovery as a result of the three-stage process of rescue archaeology are a couple of Pre-Roman Iron Age burials at Alu, which laid under the clearance heap of late prehistoric and historical times.

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