RADAR technology is being used to unlock the secrets of the Abbey Meads Roman site.
Two archaeologists are surveying the area using a ground-penetrating radar.
The device will provide the most detailed picture ever of the four large stone structures which once stood at the site.
And perhaps it will solve the mystery of what this huge complex was used for.
To the untrained eye the open space at Groundwell Ridge, on Pennine Way, looks like nothing more than hilly scrubland.
But surveys have revealed it to be one of the most important Roman sites in Britain and one of only two of its kind in the country.
Hidden beneath the grass are the foundations of four large stone structures and an extensive network of water features, walls and paths.
One theory is that it was a temple complex built to worship a water god.
This is borne out by its position at the site of a natural spring.
English Heritage archaeological scientists, brothers Paul and Neil Linford, have spent two days this week using a £30,000 radar device to survey the area where the largest building on the site once stood.
The 25-metre by 15-metre structure is thought to have been a bathhouse.
The Linfords will present their results at Abbey Meads Primary School on Sunday as part of a display being held to mark National Archaeology Day.
They hope by that time to have built up a detailed map of the building's foundations and to have a good idea of what it was used for.
Neil Linford said: "When I first got involved with this site in 1996 the idea was we'd do a survey and find out what this site was.
"The more we have surveyed it the more mysteries we have uncovered.
"It seems each thing we have found has raised as many questions as it has answered.
"That's what makes it such an interesting site and almost unique."
Whatever the purpose of the Groundwell Ridge complex, its size means it was an extremely important part of Roman-era mid-west England.
Before Swindon even existed it would have been the most important settlement between Cirencester and Wanborough.
Silver coins, plates and pottery recovered from the area will be on display at Abbey Meads Primary School between 11am and 4pm on Sunday. There will also be guided visits. Places are limited and must be booked in advance.
For more information call 466556.
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