STOCKHOLM – A dozen centuries-old shipwrecks — some of them unusually well-preserved — have been found in the Baltic Sea by a gas company building an underwater pipeline between Russia and Germany.

The oldest wreck probably dates back to medieval times and could be up to 800 years old, while the others are probably from the 17th to 19th centuries, Peter Norman of Sweden’s National Heritage Board said Tuesday.

“We have only seen pictures of their exterior. Many of them are considered to be fully intact,” Norman said.

The latest discovery was made during a search of the seabed east of the Swedish island of Gotland by the Nord Stream consortium, which is building a 750-mile pipeline. The 12 wrecks were found in a 30-mile-long, 2-mile-wide corridor.

Swedish marine archaeology experts analyzed pictures of the wrecks and determined that they could be of high historic value.

“The content can tell us a lot about everyday life during that time,” Norman said.