By Duncan Kennedy BBC News, Rome 3 May 2009 Rome's underground Christian, Jewish and pagan burial sites, the Catacombs, date back to the 2nd Century AD. There are more than 40 of them stretching over 170km (105 miles). But, until now, they have never been fully documented, their vast scale only recorded with handmade maps. That is now changing, following a three-year project to create the first fully comprehensive three-dimensional image using laser scanners. A team of 10 Austrian and Italian archaeologists, architects and computer scientists have started with the largest catacomb, Saint Domitilla, just outside the Italian capital. The tunnels, caves, galleries and burial chambers of Saint Domitilla stretch for about 15km (9 miles) over a number of levels. At a time when Christians, in particular, were persecuted, the Catacombs became a relatively safe place to bury the dead. The soft, volcanic tufa rock was an especially workable, yet durable, material that was burrowed out over the course of nearly three centuries. Yet, because of concerns about safety, only about 500m (1,640ft) are accessible to the public today. Scanner The new, moving, images of this entire underground system will change all that and open up this beautiful subterranean world in a way that it has never been seen before. The leader of the project, Dr Norbert Zimmerman of the Vienna Academy of Sciences, was behind the idea to use laser scanners to record every part of the Catacombs. His scanner, which looks like a cylinder on a tripod, stands a metre or so high and is a piece of kit you usually find in the construction industry. Gone are the days when archaeologists just used shovels, brushes and sieves to unearth the past. The scanner has been placed in hundreds of different locations in the Catacombs. It turns slowly, sending out millions of light pulses that bounce off every surface they come into contact with. The light pulses rebound back into the scanner and are recorded on a computer as a series of white dots, known as a "point cloud". Gradually, every wall, ceiling, and floor is bombarded with the dots, enabling the computer to build up a picture of each room. Eventually, the computer completes a 360-degree, three-dimensional, moving image of that room, with every surface looking like it is made up of small white dots. At the same time a camera on the scanner takes a picture of each surface. That information is also fed into the computer enabling colour to be added to "fill in" the dots. 'Real data' When the process is finished, it looks like an actual film of the particular room in question. In all, four billion dots were recorded, enabling practically the whole catacomb to be documented in this way. Only a handful of small spaces were left out because it simply was not possible to get the scanner in. The final result is astonishing. On a computer screen, you can now see the whole underground complex. Using different buttons on the key pad, you can zoom in on the tunnels. You can travel "through" walls, down corridors and into chambers, giving the first real sense of its beauty, scale and detail. Paintings on walls, which have not been seen in nearly 2,000 years, are now visible - their colours vivid and clear. "It is not a virtual image, it is not animation - what you are seeing is real data," says Mr Zimmerman. I ask him why he did not just video the whole thing. "Well, you could have filmed each room. But that would not have given you the ability to 'travel' through the catacomb in a way that the scanned images allow," he says. "Its moving, 3D flexibility, gives you the chance to compare areas, to assess the ways the Catacombs were developed over time, to analyse how and why those who built them did what they did," he adds. "That's never been possible before." 'Big job' Mr Zimmerman and his team have nearly completed their work on the Saint Domitilla catacomb. It is now back to Vienna to study the images in more detail. Dr Zimmerman says much of the work will be made available to the public. Examining the images from the Saint Domitilla catacomb alone will keep them busy for the next year or so. He has no plans to scan all the Catacombs. "That is a big job, but it may well be needed if we are to really understand this incredible historical phenomenon and if we are to make a proper detailed study whilst these caves are still intact." "We will publish our findings to reveal, for the first time, just how impressive these tombs were and how the people of that time went to so much effort to bury their dead," he says.
