How Herod Built a Harbor
Herod’s harbor at Caesarea was the first artificial harbor in the ancient world. It is shown here (1), partially reconstructed (but not drawn to exact scale) as it probably appeared in 10 B.C. when Herod completed it. The reconstruction is based on descriptions of harbor construction by Vitruvius (On Architecture), and on the descriptions of Caesarea’s harbor by Josephus in The Jewish War and Jewish Antiquities and on archaeological remains discovered in recent years.
The harbor was formed by two breakwaters, built on concrete foundations, extending up to 1,500 feet into the Mediterranean Sea. The larger southern breakwater enclosed an inner basin. The northern breakwater was 150 feet wide; the southern breakwater was approximately 200 feet wide. Between the two breakwaters was the 60-foot-wide entrance to the harbor. Outside the entrance to the harbor, in the foreground, stood three large concrete piers resting on the sea bottom. The two on the right were said by Josephus to have been joined together as part of a platform for monumental sculpture. The single tower on the left also supported monumental sculpture (2). Ships entering the harbor would have passed between the two groups of sculpture. Based on evidence from other harbors and from the writings of Josephus, it is possible, although far from certain, that a tower stood on the end of one or both of the breakwaters flanking the entrance to the harbor. It is likely that one of these towers served as a lighthouse. In times of siege a chain may have stretched between the ends of the breakwaters to prevent the passage of ships. In the summer of 1982, divers discovered a concrete foundation block at the northwest corner of the terminus of the northern breakwater and a second block—not connected to this breakwater—20 feet north of the first one. The second block formed the foundation of the outer tower seen on the left.
The aim of Herod’s engineers was to build an artificial anchorage where there was no natural harbor to shelter ships. They did this by laying immense concrete blocks on the sea bottom, starting at the shore and building seaward from the blocks already in place.
First a wooden form was constructed and placed on the sea bottom. The bottommost corner of one of these wooden forms was found with the concrete block that had been poured into it (3). The sides of the form consisted of a double wall of planks. Between the inner and outer parts of this double wall was concrete packing, poured into the double wall and allowed to set in order to strengthen the form before it was lowered into the sea.
The drawing (4) is a detail of the wooden remains in situ; the drawing (5) illustrates the simple lap joint that connected the two beams. Horizontal and vertical wooden tie beams added stability to the form.
The tie beams and the rest of the wooden form are gone—destroyed by shipworms and decay—but the images of the wooden vertical and horizontal tie beams remain in the concrete block. An exact drawing (6) of the top surface of the two blocks discovered last summer—shows the block at the end of the northern breakwater (right) and the block forming part of the base of the tower outside the harbor entrance at the end of the northern breakwater (left). The block from the breakwater measures 49 feet by 39 feet by 5 feet; the block from the tower foundation was only partially excavated. Shown in red are the holes that once contained the vertical wooden members of the form’s inner structure. Seen in yellow are the cavities left in the block by some of the horizontal wooden tie beams that joined the vertical pieces.
From this information we are able to reconstruct the probable appearance of a form (7). Here the artist has drawn one complete form in the water, waiting to receive concrete. It seems likely that the concrete would have been poured through large tubes located on the upper level of the breakwater where a person stands and perhaps also from barges anchored nearby. This upper level was constructed of stones and smaller concrete blocks placed on top of a previously poured concrete form identical to the one shown to its right.
By using each concrete block as a base from which a new form could be put in place, the breakwaters were gradually extended to their final length.