One of the most advanced and sophisticated computer-based analyses of an ancient landscape in Europe is taking the excavation out of discovery

To dig or not to dig?


Archaeologists at Wroxeter in Shropshire have uncovered spectacular remains of a Roman settlement inhabited continuously for 400 years without removing an ounce of the soil that buries it.

Using an assortment of remote sensing techniques, some of them applied to archaeological investigation for the first time, an international team of archaeologists, scientists and volunteers has discovered the features of a thriving Roman centre including shops, houses, streets, temples, churches, an aqueduct with a capacity of about two million gallons a day and a network of channels that supplied water to the houses.

The three-year Wroxeter Hinterland Project began in September 1994 under the direction of the University of Birmingham. It is the culmination of over forty years of archaeological research and training at Wroxeter and has incorporated the work of British and American universities, researchers from international commercial companies and government institutions devoted to the preservation of the cultural heritage.

The settlement was known to the Romans as Viroconium Cornoviorum and founded by the Fourteenth Legion as a fortress around AD 60. The first plans of it were drawn up from aerial photographs taken after World War II and the excavation of a tiny fraction of the site amounting to five percent of the total area which yielded extensive remains of the city baths and forum.

Now, after two years’ research with remote sensing techniques, eighty percent of the 140-acre city has been investigated leading to the triplication of the estimated number of inhabitants.

The Japan Division of the University of Miami and the Nara Cultural Properties Research Institute, Japan have pioneered the archaeological application of Ground Penetrating Radar (GPR) on a large scale. They have developed techniques for the “time-slicing” of data from GPR surveys which have provided a sequence of archaeological site plans to a depth of 1.5 metres at Wroxeter.

GPR investigation aims microwaves, or extremely high frequency waves, downwards into the ground where some of them bounce against buried archaeological remains and head back towards the machine that launched them. The returning waves are received by an antenna built into the GPR machine and recorded by a computer. Since it is known how fast microwaves travel in soil, the time it takes waves to return reveals the depth of the buried remains. The whole GPR apparatus is wheeled along parallel lines laid out on-site and takes readings systematically at one metre spacings.

This survey produces hundreds of vertical readings. To create a picture of remains at one particular depth, the readings are dissected horizontally and the data existing at that level is recorded. The one metre gaps between the original vertical slices are filled in with digital image processing.

Radar-sensing techniques were used last year to detect an older version of the Great Wall of China from the space shuttle. They have been applied to extended archaeological research for the first time at Wroxeter and have yielded such encouraging results that they seem set to become an essential component of archaeological research where adequate technology allows.

Scientists from the Centre Nationale de la Recherche Scientifique (CNRS) at Garcy in France, have carried out experimental Resistivity research at Wroxeter using new equipment which allows a much more rapid and extensive survey than other resistivity machinery currently in use. With this technique, electrodes are buried in the ground and a continuous current is passed between them. A buggy carrying an automated twin-probe array apparatus is pulled along the surface, takes rapid readings and by determining the degree of resistance the electric current is encountering underground—walls are highly resistant, ditches are good conductors—is able to create a two-dimensional image of the site. The method, which can even locate details such as individual column bases, has been applied for a number of years, but it is only recently that technology has allowed its use on such a large scale.

English Heritage’s Ancient Monuments Laboratory has been conducting extensive Magnetometry Surveys by analysing distortions in the earth’s magnetic field caused by the density of buried objects. The site is scanned using a device that is highly sensitive to magnetic fields. This technique has revealed the most extensive plans of the whole city.

Using this type of survey, Geophysical Surveys of Bradford, a commercial company specialising in archaeological geophysics have uncovered evidence of a fire which swept through the city in its heyday. The effects are detectable in a complete reversal of the magnetometric readings from those found in the rest of the site. This may be the same fire dated to AD 180 detected by excavation in the market area.

Experimentation with depth estimation work through Seismic Prospecting—the investigation of the depth and character of buried remains by noting the travel times of reflected artificial shock waves—has also been carried out by this company.

Hyperspectral Scanning, a remote scanning technique conducted from an aeroplane, is being applied to archaeological research for the first time. The method usually determines changes in patterns of vegetation and soil by scanning the countryside and registering wavelengths not visible to the human eye. The National Environment Research Council (NERC) is using this method at Wroxeter to detect changes in vegetation possibly determined by underlying remains.

Accumulated data from all these and other techniques being used at Wroxeter is fed into computers and transformed into highly detailed site-plans. Excavating to draw up comparable site-plans would take millions of pounds and over a hundred years. Remote sensing research will complete the survey of Viroconium by late 1997. The project has been comparatively cheap, the work being financed principally through a major award of £139,690 from the Leverhulme Trust and the contributions of the participating bodies.

Simon Buteux, Project Manager and director of field archaeology at Birmingham University points to computer-based techniques as an important method of preserving the cultural heritage: “In the process of excavation, archaeologists destroy much of their evidence, even as they seek to record and understand it”. The example of Pompeii, roughly the same size as Viroconium, is a powerful reminder of the dangers of excavation. In the Campanian site, large areas are overgrown with brambles and weeds, overrun by hordes of undisciplined schoolchildren and eroded by wind, rain and acidic pigeon droppings.

However, without excavation, artefacts escape detection and cannot be recovered, nor can floor mosaics or wall paintings be discovered. If the archaeologists want to see Viroconium for real, they are still going to have to dig. The difference is that for the first time they will know they are digging in the right place. Targeted excavation on a small scale can answer carefully formulated questions and control the problem of preservation. Mr Buteux would now like to see careful excavation take place subject to endorsement from English Heritage.

Work on the production of a virtual reality experience of the city is just beginning in Birmingham with £91,062 from British Telecom. It may be the only chance we get of actually “seeing” the ancient Roman settlement.

Originally appeared in The Art Newspaper as ‘To dig or not to dig?'