S1, E4: During excavation for the deepest submerged tunnel in the world, engineers in Istanbul uncovered a hidden past: a preserved ancient harbor. It is the biggest maritime discovery in history, and to date, more than 30 shipwrecks from the Byzantine era have been recovered. With new findings every day-including stone foundations from a settlement dating back 8,000 years-construction of the tunnel has come to a halt, and the delay is costing the engineers millions. Now, National Geographic goes on site to one of the largest archaeological excavations ever undertaken and grants viewers behind-the-scenes access to this heated battle between modernizers and historians.