The oldest known shipwreck in the Indian Ocean has been sitting on the seafloor off the southern coast of Sri Lanka for some 2,000 years. In just a couple of weeks, scuba-diving archaeologists will embark on a months-long excavation at the site, looking for clues about trade between Rome and Asia during antiquity.

The wreck lies 110 feet (33 meters) below the ocean's surface, just off the fishing village of Godavaya, where German archaeologists in the 1990s found a harbor that was an important port along the maritime Silk Road during the second century A.D.

The sunken ship, discovered only a decade ago, doesn't look like your stereotypical skeletal hull. Instead, what archaeologists are dealing with is a concreted mound of corroded metal bars and a scattering of other ancient cargo, including glass ingots and pottery, that have tumbled around on the seafloor for hundreds of years amid strong currents and perhaps even the occasional tsunami. [See Haunting Images of Shipwrecks Across the Globe]....