When the divers ducked beneath the surface, they knew their target: a mysterious iron cauldron at the bottom of England’s River Wear. They had no idea how the vessel had ended up there, though they were fairly certain it had been underwater for hundreds of years. Their mission was to recover it from the watery darkness and bring it back to the surface. After freeing the artifact from debris, the divers secured it in thick green netting inside a metal cage. Team members on a recovery craft above then slowly pulled it up into the late morning sun. It arrived...