Remnants of a breakwater built 2,000 years ago suggest that the Romans knew how to make massive concrete placements underwater. At the long-abandoned sunken harbor in Caesarea, Israel, archaeological divers found massive concrete blocks, some as large as 15x11x2 yards. They also found parts of timber forms still in place at the base of the concrete. The blocks still carried impressions of wood forms, and tests confirmed that the concrete had hardened in the water.