Coastal Engineering in the Classical World

Another excerpt from the Coastal Engineering Manual, this time concerning coastal development and construction in the Greco-Roman world and before that.  It should be of interest to ancient history aficionados and engineers alike.

I-3-1.  Ancient World

The history of coastal engineering reaches back to the ancient world bordering the Mediterranean Sea, the Red Sea, and the Persian Gulf.  Coastal engineering, as it relates to harbours, starts with the development of maritime traffic, perhaps before 3500 B.C.  Shipping was fundamental to culture and the growth of civilization, and the expansion of navigation and communication in turn drove the practice of coastal engineering.  The availability of a large slave labour force during this era meant that docks, breakwaters, and other harbour works were built by hand and often in a grand scale similar to their monumental contemporaries, pyramids, temples, and palaces.  Some of the harbour works are still visible today, while others have recently been explored by archaeologists.  Most of the grander ancient harbour works disappeared following the fall of the Roman Empire.  Earthquakes have buried some of the works, others have been submerged by subsidence, landlocked by silting, or lost through lack of maintenance.  Recently, archaeologists, using modern survey techniques, excavations, and old documents, have revealed some of the sophisticated engineering in these old harbours.  Technically interesting features have shown up and are now reappearing in modern port designs.  Common to most ancient ports was a well-planned and effectively located seawall or breakwater for protection and a quay or mole for loading vessels, features frequently included in modern ports (Quinn  1972).

Most ancient coastal efforts were directed to port structures, with the exception of a few places where life depended on coastline protection.  Venice and its lagoon is one such case.  Here, sea defenses (hydraulic and military) were necessary for the survival of the narrow coastal strips, and impressive shore protection works built by the Venetians are still admired.  Very few written reports on the ancient design and construction of coastal structures have survived.  A classic treatise by Vitruvius (27 B.C.) relating the Roman engineering experience, has survived (Pollio, Rowland, and Howe 1999).  Greek and Latin literature by Herodotus, Josephus, Suetonius, Pliny, Appian, Polibus, Strabo, and others provide limited descriptions of the ancient coastal works.  They show the ancients’ ability to understand and handle various complex physical phenomena with limited empirical data and simple computational tools.  They understood such phenomena as the Mediterranean currents and wind patterns and the wind-wave cause-effect link.  The Romans are credited with first introducing wind roses (Franco 1996).

I-3-2.  Pre-Roman Times

Most early harbours were natural anchorages in favourable geographical conditions such as sheltered bays behind capes or peninsulas, behind coastal islands, at river mouths, inside lagoons, or in deep coves.  Short breakwaters were eventually added to supplement the natural protection.   The harbours, used for refuge, unloading of goods, and access to fresh water, were closely spaced to accommodate the safe day-to-day transfer of the shallow draft wooden vessels which sailed coast-wise at speeds of only 3-5 knots.

Ancient ports can be divided into three groups according to their structural patterns and the development of engineering skill (Frost 1963).

a. The earliest were rock cut, in that natural features like offshore reefs were adapted to give shelter to craft riding at anchor.

b. In the second group, vertical walls were built on convenient shallows to serve as breakwaters and moles.  Harbours of this type were in protected bays, and often the walls connected with the defences of a walled town (for example, ancient Tyre on the Lebanese coast).  Often these basins were closable to traffic using chains to prevent the entry of enemy ships (Franco 1996).

c. The third group were harbours 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 harbour 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 harbour 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 harbour.  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 harbour.

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 harbour of this era was the first harbour 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 harbour.  Alexander the Great and his Greek successors rebuilt the harbour (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 harbours 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 harbour 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-3-3.  Roman Times

The Romans introduced many revolutionary innovations in harbour design.  They learned to build walls underwater and constructed solid breakwaters to protect exposed harbours.  They used metal joints and clamps to fasten neighbouring blocks together and are often credited with discovering hydraulic cement made with pozzolanic ash obtained from the volcanic region near Naples, which hardens underwater.  Frost (1963) notes that the Greeks had used hydraulic cement long before the Romans.  The Romans replaced many of the Greek rubble mound breakwaters with vertical and composite concrete walls.  These monolithic coastal structures could be built rapidly and required little maintenance.  In some cases wave reflection may have been used to prevent silting.  In most cases, rubble or large stone slabs were placed in front of the walls to protect
against toe scour.  The Romans developed cranes and pile drivers and used them extensively in their construction.  This technology also led them to develop dredges.  Another advanced technique used for deep-water applications was the watertight floating cellular caisson, precursor of the modern day monolithic breakwater.  They also used low, water-surface breakwaters to trip the waves before they reached the main breakwater.  The peculiar feature of the vertical wall breakwater at Thapsus (Rass Dimas, Tunisia) was the presence of vents through the wall to reduce wave impact forces.  This idea is used today in the construction of perforated caisson breakwaters (Franco 1996).

Using some of these techniques, the Romans built sophisticated breakwaters at Aquileia, Italy (ca. 180 B.C.), and at Caesarea, Israel (ca. 20 B.C.).  The south-western breakwater at Caesarea contained a “forebreakwater” that acted as a submerged reef that “trips” the wave causing it to break and dissipate energy before encountering the main breakwater  (Inman 2001).

The largest man-made harbour complex was the imperial port of Rome;  the maritime town at the mouth of the Tiber River was named Portus (The Port).  It is now some four km from the sea, partly buried under Rome-Fiumicino airport.  Despite its importance to the capital of the empire, (300,000 tons/year of wheat from Egypt and France), the harbour always suffered siltation from the river.  Trajan, who also built the ports of Terracina and Centumcellae, built Portus’ inner hexagonal basin.  The port of Centumcellae was built just to serve his villa at a site with favourable rocky morphology.  A grandiose engineering project between 107-106 B.C. created a sheltered bathing and boating retreat.  Slaves from all parts of the empire excavated a harbour and hauled in massive stones to create an artificial harbour to dampen the force of the waves.  After the decline of Portus, it became, and remains, the Port of Rome.  After remaining unchanged for over 1,000 years, the inner Roman Basin, which was dredged from rock (200,000 m³ or 260,000 yd³), is still in use.  Roman engineers also constructed harbours in northern Europe along the main waterways of the Rhine and Danube and in Lake Geneva.  They became the first dredgers in the Netherlands to maintain the harbour at Velsen.

Silting problems here were solved when the previously sealed solid piers were replaced with new “open”- piled jetties.  In general, the Romans spread their technology throughout the western world.  Their harbours became independent infrastructures, with their own buildings and storage sheds as opposed to the pre-Roman fortified city-enclosed harbours.  They developed and properly used a variety of design concepts and construction techniques at different coastal cites to suit the local hydraulic and morphological conditions and available materials (Franco 1996).

The Romans also introduced to the world the concept of the holiday at the coast.  The ingredients for beach holidays were in place:  high population density coupled with a relatively high standard of living, a well-established economic and social elite, and a superb infrastructure of roads.  From the end of the republic to the middle of the second century of the empire, resorts thrived along the shores of Latium and Capania, and an unbroken string of villas extended along the coast from the seashore near Rome to the white cliffs of Terracina.  Fine roads connected these resorts to the capital, allowing both the upper crust and the masses to descend from sultry and vapour-ridden Rome to the sea.  For five hundred years, the sybaritic town of Baiae reigned as the greatest fashionable beach resort of the ancient world.  Seneca the Younger called Baiae a“vortex of luxury and a harbour of vice,” an alluring combination that Romans found irresistible (Lencek and Bosker 1998).

References:

• Empereur, J. Y.  1997.  “The Riches of Alexandria.” Transcript of a 1997 Interview on NOVA Online, http://www.pbs.org/wgbh/nova/sunken/empereur.html (28 Aug 2000).
• Franco, Leopold.  1996.  “History of Coastal Engineering in Italy,” History and Heritage of Coastal Engineering, American Society of Civil Engineers, New York, NY. pp 275-335.
• Frost, H.  1963.  Under the Mediterranean, Marine Antiquities.  Prentice-Hall, Englewood Cliffs, N.J.  p 278.
• Inman, D. L.  1974.  Ancient and Modern Harbors:  a Repeating Phylogeny. Proceedings of the 14th Coastal Engineering Conference, Copenhagen, Denmark, June 1974, American Society of Civil Engineers, Reston, VA, pp. 2049-2067.
• Inman, D. L.  2001.  History of Early Breakwaters.  Association of Coastal Engineers Newsletter, Alexandria, VA.
• Lencek, L., and Bosker, G.  1998.  The Beach:  The History of Paradise on Earth.  Viking, New York, 310 p.
• Quinn, Alonzo DeF.  1972.  Design and Construction of Ports and Marine Structures, Second Edition, McGraw-Hill Book Company, New York, N.Y., 611p.