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This is a diagram looking southeast at the hexagonal basin/harbor that was built by the Roman Emperor Trajan (r. A.D. 98–117). It covers 80 acres and its bottom was paved.
Note that on the banks of the basin there were spaces for ships to dock and offload their cargo. In addition, on the east side was a temple—somewhat like the harbor that Herod the Great had built 100+ years earlier at Caesarea.
At the bottom of the picture is where the earlier, larger, basin that was built by Claudius was built.