For 500 years, the Baltic Sea held in its depths a tall ship of the Renaissance era . Around the time the ship sank, Columbus was discovering the New World. His fleet vanished long ago. But the Renaissance vessel suddenly reappeared recently, remarkably well preserved in the icy Baltic waters.

The first hint of its existence came in 2009, when a sonar survey by the Swedish Maritime Administration registered an anomalous blip on the Baltic seafloor. Then, early this year, a robotic camera, employed by a commercial team surveying an undersea route for a natural gas pipeline, illuminated not the gooey seabed but a mysterious hulk.

In March, an international team of scientists lowered a pair of tethered robots to explore and document what turned out to be the Renaissance sailing vessel.

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“It’s amazing,” said Rodrigo Pacheco-Ruiz, a maritime archaeologist at the University of Southampton, in Britain, who led the investigation. “We’re still a little bit over the moon.”