Watch Great Expeditions online: Episode 4 Ghost Ships of the Black Sea

Seven years ago, on his third trip to the Black Sea, Dr. Robert Ballard discovered a miraculously well-preserved Byzantine shipwreck, but his team could only take pictures. Now, Ballard returns with state-of-the-art technology and a revolutionary $1.5 million robot known as "Hercules" to excavate two shipwrecks for the first time ever, including one of the most pristine ancient vessels ever found. Ballard and his team have only two weeks, so they must work in perfect precision on their hunt for the Ghost Ships of the Black Sea

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