Alfred Merlin was digging for Roman remains in Tunisia in 1907 when sponge-divers identified mysterious remains - stone columns, just off-shore in the Mediterranean. Was this the legendary lost city of Atlantis? But when beautifully crafted Roman works of art were salvaged from the site, Merlin came to an even more intriguing conclusion: These were the remains of a Roman shipwreck. The Mediterranean, he knew, was the highway of the ancient world - water was the only efficient way to transport heavy goods quickly throughout the Empire. And when greedy traders overloaded their ships, the resulting disasters left behind a gift for archaeologists 2000 later. Understand where the ships were going and what they were taking, and you could decode the whole of the ancient world. And so Alfred Merlin created a whole new discipline: marine archaeology. At first it was exhausting and extremely dangerous work. Divers in the cumbersome suits with lead boots and copper helmets depended on a steady stream of air pumped from the surface. Many suffocated or died in agony from the bends. But the rewards were fabulous: individual artworks and the revelation of a trade network that saw building materials and luxuries crossing hundreds of miles of sea to construct new colonies in the image of Rome. This film shows the pioneers at work in Merlin's time and their successors today, faced with the same challenges of salvage and preservation, and even using some of the same methods.