Ghost of a flea

There could be as many as 100,000 shipwrecks in the Baltic Sea, said Stefan Wessman, a marine archaeologist at Finland's Maritime Museum. "The Baltic Sea has huge potential, and I believe this is recognized by scientists internationally," he said. "There is nothing comparable to it in the world." It's not just the number of Baltic wrecks that enthralls underwater researchers like Wessman and Mass. It's that so many are well-preserved -- veritable time capsules certain to expand understanding of the past.

"It's hard to imagine something telling us more," said Wessman, speaking by telephone from Helsinki. "You can get a whole cross-section of a society on one ship. The only equivalent on land I can think of is if you found a whole ancient library buried intact."