EM 1110-2-1100 (Part I)
30 Apr 02
b. In the second group, vertical walls were built on convenient shallows to serve as breakwaters and
moles. Harbors of this type were in protected bays, and often the walls connected with the defenses
of a walled town (for example, ancient Tyre on the Lebanese coast). Often these basins were
closeable to traffic using chains to prevent the entry of enemy ships (Franco 1996).
c. The third group were harbors that were imposed on even unpromising coasts by use of Roman
innovations such as the arch and improved hydraulic cement. Projects like this required the
engineering, construction, and financing resources of a major empire.
All ancient ports had one thing in common: they had to be kept clear of silt at a time when mechanical
dredging was unknown. This was accomplished by various means. One was by designing the outer parts of
the harbor so that they deflected silt-bearing currents. The second was by allowing a controlled current to
flow through the port or by flushing it out when necessary by means of channels. For example, at Sidon, a
series of tanks (like swimming pools) were cut into the harbor side of a natural rock reef. The tanks filled
with clear water that was held in place with sluice gates. When the gates were opened, currents of clear water
would flush the inner harbor. Documentary and archaeological evidence show that both Tyre and Sidon were
flourishing and powerful ports from the Bronze Age through the Roman era and must therefore have been
kept clear of silt for over a thousand years (Frost 1963). Another method of preventing silt consisted of
diverting rivers through canals so that during part or much of the year, the flow would enter the sea at location
well away from the harbor.
The origins of breakwaters are unknown. The ancient Egyptians built boat basins with breakwaters on the
Nile River at Zoser's (Djoser) step pyramid (ca. 2500 B.C.) (Inman 2001). The Minoans constructed a
breakwater at Nirou Khani on Crete long before the explosion of Santorini (Thera) in ca. 1500 B.C. The
breakwater was small and constructed of material taken from nearby dune rock quarries (Inman 1974,
Figure 4). In the Mediterranean, size and sophistication of breakwaters increased over time as the Egyptian,
Phoenician, Greco-Macedonian, and Roman civilizations developed and evolved. Breakwaters were built
in China but generally at a later date than in the Mediterranean.
Probably the most sophisticated man-made harbor of this era was the first harbor of Alexandria, Egypt, built
west of Pharos Island about 1800 B.C. by the Minoans. The main basin, built to accommodate 400 ships
about 35 m in length, was 2,300 m long, 300 m wide and 6-10 m deep. Large stone blocks were used in the
many breakwaters and docks in the harbor. Alexander the Great and his Greek successors rebuilt the harbor
(300-100 B.C.) in monumental scale. The Island of Pharos was joined to the mainland by a 1.5 km
breakwater with two openings dividing two basins with an area of 368 hectares (910 acres) and 15 km of quay
front. Alexandria is probably best known for the 130m-high lighthouse tower used to guide ships on a
featureless coast to the port from 50 km at sea. The multi-storied building was built with solid blocks of stone
cemented together with melted lead and lined with white stone slabs. Considered one of the Wonders of the
Ancient World, it eventually collapsed due to earthquakes between 1326 and 1349 (Franco 1996, Empereur
1997).
Another feature of the Greek harbors was the use of colossal statues to mark the entrances. Colossal statues
of King Ptolemy, which stood at the base of the lighthouse, have been found with the lighthouse debris.
Historians report the most famous harbor statue was the 30 m high Colossus of Rhodes, which stood on the
breakwater heads. Three ancient windmill towers are still surviving upon the Rhodes breakwater (Franco
1996). Frost (1963) notes that the Greeks had used hydraulic cement long before the Romans.
I-3-2
History of Coastal Engineering
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