National Geographic : 1987 Feb
(1 7 rr ~9 ~r: " HE KING... overcame nature," wrote the Jewish L historianJosephus. Crucialto success was a corps of professionaldivers. Although capable offree diving 90 feet or more, they only worked in depths of nine to twelve feet at Caesarea.Ancient ships drew as little as six feet. Concrete blocks, some weighing 50 tons, anchoredthe north breakwater.Double walled wood forms constructed nearshore were towed into position over a foundation of boulders on the sandy bottom. Waterproof mortarpacked between the double walls sank the form. Workers lowered concrete in baskets. When set, the foundation was paved with stone. A rubble barrierat the seawall barredundertrenching currents. Volcanic ash, key ingredient in hydraulic concrete, and wood for forms were imported, probablyfrom Italy. "There was no room for mistakes," the authorsays. jj'7I , !