Its name and image are among the most familiar in the world. More than a million people travel to Britain's Salisbury Plain every year to see it.

The ancient monument known as Stonehenge is an enduring object of fascination partly because of its mysteries: who built it, how did they build it, and why? Now, as a result of a five-year research project, there are answers to at least some of the lingering questions about the iconic edifice, revealed in the Smithsonian Channel two-hour special "Stonehenge Empire," which premieres on Sept. 21.

Relying on experts from the University of Birmingham in the U.K. and the Ludwig Boltzman Institute in Austria, the Stonehenge Hidden Landscapes Project used modern technology to analyze the monument and 5-and-half square miles of surrounding landscape to map above- and below-ground features and structures, revealing many previously unknown objects that pre-date the circle of stones. The documentary details these findings and uses CGI projections and recreations to paint a bigger picture of the landscape and the civilizations that inhabited it, putting Stonehenge in a broader context of space and time.

Professor Vincent Gaffney, chair of Landscape Archaeology and Geomatics at the University of Birmingham and the leader of the project, is featured in the documentary. He previews what you can expect to learn

MNN: Why is Stonehenge so enduringly alluring?

Vincent Gaffney: Almost certainly, its iconic form, its size and age. It clearly attracted attention during our earlier periods, which could not explain how such things were made. They became "the work of giants," moved by Merlin. After that, the myths grew and today many people continue to need to relate to Stonehenge, because it has endured.  

How long have you been interested in it and been studying it?

My very first job after university in 1980 was on the Stonehenge Environs Project with Julian Richards (of "Meet the Ancestors" fame). In the late '90s, I started my first [book] project looking at the interrelationships with monuments around Stonehenge, "Stonehenge Landscapes: Journeys Through Real-and-Imagined Worlds."

How did the Stonehenge Hidden Landscapes Project come about?

The book convinced me it was not enough to look at the known monuments. We needed to look in between to work out where things were not, as well as where they were. The only problem was the technology to do it. My brother Chris — he's also an archaeologist — and I considered the possibilities of extensive geophysics in 2007 when the first GPS guided equipment arrived, but it wasn't until the Ludwig Boltzmann Institute for Archaeological Prospection and Virtual Archaeology was formed and provided a pan-European consortium in which we could pool resources for major archaeological research at a massive scale that the opportunity arose to carry out this work

Explain how the different mapping technologies were put to use in surveying the site and gave you a 3-D picture of the visible area and below it.

No single technology gives you everything. We use three major technologies and 15-plus instruments at variable speeds and resolutions: Magnetometer, ground penetrating radar and laser scanning. All provide a different response to archaeological remains. Some are 3-D rather than 2-D, and the sum of the parts is greater than the whole when these are integrated for interpretation.

A 3-D reconstruction imagines what Stonehenge may've looked like thousands of years ago

A 3-D reconstruction imagines what Stonehenge may've looked like thousands of years ago.

Did the findings surprise you? What were the most significant? What surprised you most?

The significance really is the fact that the new map is almost seamless and that the majority of the area is no longer "terra incognita" or simply blank. There were hundreds and perhaps thousands of features and sites that had either been unrecorded or were not mapped properly. Should we have been surprised? Possibly not. Cumulatively, most European landscapes have all been used and modified. What perhaps did surprise me is the mounting evidence for smaller processional routes and minor shrines in the landscape — also possibly parts off processional routes. This really indicated that Stonehenge was probably a focus of activity and that many people and not just the chosen few may have been progressing or circling through it.

Was the project intended to be filmed from the start, or did that come later?

The documentary came later in the project. However, we had always imagined that the results might have a wider audience. Who isn't interested in Stonehenge?

How does this change how we think of Stonehenge and the people who built it?

Society was more complex in its relationship with the monument. It wasn't alone and isolated from the populace. It was always a "public" monument.

A 3-D image presents a possible version of a completed Stonehengde

A 3-D image presents a possible version of a completed Stonehenge.

What unsolved mysteries about Stonehenge intrigue you most, and is it possible to solve them? How would you go about it?

There are may other mysteries or things we would like to know about Stonehenge. How it started — it was probably not simply the monument we see today. The first monuments were a row of massive pine posts that may have looked like totem poles. However, these were dated to 9,000 B.C., some 6,000 years before "The Stones." This is the period known as the Mesolithic, the last period when hunter-gatherers, not farmers, lived in Britain (about 10,000-6,000 B.C.). We need to explore this very ancient period of land in order to understand how the site grew and developed. Who knows, we may even find some clues in our current data sets. We still need another year at least to analyze the data.

What other iconic sites would you like to explore/survey in this way? Any plans to do so?

There are many sites worthy of exploring using these technologies. We'll have to think what should be done next after we publish this data. If we don't do that, the exercise will not have been completed, and that would be a tragedy!

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'Stonehenge Empire' reveals monumental secrets
Documentary chips away at the mysteries surrounding the world's most famous monument.