Construction and structure of ancient Mesopotamian ziggurats

History Of Construction 26 Buildings

History of the Construction of 12 Buildings

Construction of the Ziggurat

According to Gwendolyn Leick, an expert in Mesopotamian archaeology, "No ziggurats have survived enough to reconstruct either access or the high temple with any certainty" (Leick 108). Despite this lack of material specificity about what was on top of the ziggurat, ancient ziggurat remains give important clues about their material structure, their building process, and their purpose.

Research consensus indicates that the finished ziggurat was an artificial mountain of successive platforms whose size diminished upward. Its masonry was mud brick and rubble mortared together and faced with burnt brick. Kostof writes, "The core was of mud-brick, and the thick facing of baked brick was set in bitumen mortar" (Kostof 57). The structures were solid and unsophisticated, without rooms inside them as appears later with the pyramid chambers. Nonetheless, they were carefully measured out and laid over the established walls of pre-existing dilapidated structures (Leick 13-14).

Scholars have a good idea that the ziggurat was constructed in graduated steps of distinct stages. Frankfort describes them as "staged towers with the shrine placed upon superimposed blocks of masonry, each smaller than the one below" (Frankfort 22). The reason for the staging is partially the material. Nuttgens says, "The short life of mud brick meant that constant rebuilding was required, but since the god owned the temple area in perpetuity, each successive rebuilding took place on an accumulative platform made from the debris of previous temples" (Nuttgens 24). In other words, the effect of height was achieved by subsuming the previous building, making it the new platform. Kostof describes the process this way: "The ziggurat had swelled to grandiose proportions in stages by absorbing the frames of earlier temples, which in accordance with local practice would be filled solid after serving their time, to be used as terraces for the replacement structure" (Kostof 56). The walls of the ziggurat were sloped and striped with diagonal fluting. Most ziggurats had a monumental ramp or staircase for top access. These ramps and stairs were both lateral and perpendicular to the facing of the ziggurat, and were richly carved with fierce images. Frankfort has shown, however, that some later Assyrian ziggurats did not have stair or access ramps, and access to the top may have been through sky bridges from nearby gatehouses (Frankfort 139).

According to Nuttgens, the roof was "finished off with plaited reeds or corbelling" (Nuttgens 25). He also thinks that the high priest's grave could have been embedded in the built over platform. With little doubt, the top of a ziggurat supported a temple where priestly duties were carried out. Because of the solid core, the functional activity of the ziggurat was confined to its top platform and whatever temple structure sat on it. As Leick says, "Only the highest level was used for ritual purposes, an elevated platform where the 'high temple' . . . was placed" (Leick 108). It may have had hanging gardens and trees on the upper terrace as well. The temple was considered the dwelling of a god. Herodotus describes the top-most platform as containing the bed-chambers of the gods. From this vantage point, the god could approach earth from heaven and rule over the fields and city from its landmark. Temple precincts could incorporate free-standing ziggurats.

What is impressive about the ziggurat in the history of architecture is the height it achieved. While the technology used to build ziggurats is still a mystery, it must have involved intensive human labor involving the use of ramps to build upward. Kostof discuses a stele from Ur that shows a process of sweeping soil away from the site on native rock and filling the foundation trenches with purified earth. The stele also depicts the king carrying a measuring rod and line, as well as builder's tools such as picks, compasses, and mortar baskets. This gives some indication of how the building was constructed and how it was commissioned by a king. Kostof believes that ziggurats were first built by Sumerian mountain people who came down to the flat alluvial plains to recreate atavistically their original homeland.

The ziggurat was built on a spiritual model. Its "mountain" was the communicatory stage where pilgrims or officiating priests could ascend a natural ladder into the sphere of the deities (what Kostof describes as "reverential climbing"), and the gods could likewise descend. In the building, sky and earth were linked, corresponding to Mesopotamian notions of a layered universe. Leick writes, "The names of some of the stepped pyramids, known as ziggurats, also reflect their function as a cosmic feature; the one in Babylon was called e.temen.an.ki 'House (of) the foundation of Heaven and Earth'" (Leick 108). In other words, the ziggurat reflected in its structure a cosmic geography common in the religion of the times.

Construction of Great Ziggurat of Ur (ca 2100 BC)

The Great Ziggurat of Ur is the best preserved of the thirty odd Mesopotamian tower-shrines. Its dimensions are 200 by 150 feet, and its height is estimated at 70 feet (not including the temple shrine at the top which no longer exists). McIntosh writes, "The Ur III ziggurats, epitomized by the well-preserved example at Ur itself, consisted of three staged tiers, sloping inward, with a platform at each stage, accessed by a triple stair on one side; later examples, such as that at Dur Sharrukin, might alternatively be approached via a spiral ramp" (McIntosh 201-02). Unlike the Egyptian pyramids, there has been much less study done on this ziggurat and the records are much more scant for imagining its original construction. However, there are some things scholars know.

Like other ziggurats, it was built of bricks of two kinds. Klein and Klein write, "Simple sun-dried bricks, forming the inner core of the tower, were surrounded by a thick jacket of fired or burnt bricks, eight feet thick" (Klein and Klein 34). This construction made it strong, durable, and time-resistant, which is why the building still stands (although now there is an American military base encroaching on its precinct). As with other ziggurats, it was probably built by intensive labor gangs of peasants and slaves, the same who built roads, temples, and the extensive network of irrigation canals (McIntosh 83). It served people who were once hunters now turned farmers. All the abundant groves of wheat, barley, dates, figs, grapes, as well as pastures, were thought to flow to the temple (religion) or the palace (ruler). It was the people's tithes and taxes, which were closely supervised, that paid for its construction. On top was a priestly shrine, now gone, that was likely 100 feet above ground. The shrine was dedicated to the worship of the moon god Nanna-Sin, and was likely considered a portal for the gods to descend to earth.

Who built the Great Ziggurat of Ur? Scholars are unanimous in believing it was Ur-Nammu, the monarch of the third Ur (Chaldean) dynasty whose reign was ca. 2114-2096 BCE. This is supported by inscriptions from a later date (during the time of Nabonidus), which indicate that a great ziggurat was built, but not finished during Ur-Nammu's life. Based on this inscription, Klein and Klein write, "Then Dungi, son of Ur-Nammu, came to the throne and completed the tower, known usually as the Ziggurat of Ur" (Klein and Klein 36). That Ur-Nammu built it is consistent with what we know of Ur-Nammu's building program. The founder of the third Babylonian dynasty, according to McIntosh, undertook extensive restoration and building program in religious centers, including royal mausoleums, palaces, treasuries, as well as the ziggurat of Ur (McIntosh 82-83). Foster and Foster give further evidence:

At Ur, the capital city of the new dynasty, Ur-Nammu undertook numerous building projects, some of which were shown within traditional registers on a stele depicting busy construction scenes, with workers on ladders and the king himself carrying tools. . . . At its center, he built the first ziggurat, a massive three-stage structure of solid brick, both sun-dried and baked, its corners oriented to the cardinal points, with three steep staircases joining and leading to a sanctary at the top. (Foster and Foster 62)

The great ziggurat became a model for other ziggurats at Eridu, Uruk, and Nippur. Stiebing writes, "Under Ur-Nammu, the temple-platform attained its classic form as a ziggurat, a monumental stepped pyramid-like structure with several stages or levels" (Stiebing 76).

Besides the building's immense size, it is important architecturally for its ingenious drainage system. The Chaldeans knew that bricks swell in rain or floods and could burst the walls of the ziggurat. Therefore, they employed a useful prevention technique. They pierced the walls with drainage ducts ("weeper holes") through which interior moisture could pass out. This innovation worked in conjunction with bitumen from pitch or crude petroleum used as mortar to waterproof buildings. McIntosh explains: "Courses of reed matting and layers of bitumen were interspersed between those of brick in the construction of ziggurats to counteract rising damp from the foundations, and weepholes also assisted drainage and prevented damp decay" (McIntosh 237). In other words, at every seven courses of stone, a layer of reed matting was laid and weep-holes and drainage shafts were placed, thus preserving the ziggurat from water damage.

Eventually the building fell into disrepair. Later, King Nabonidus restored the Ur ziggurat, along with other temples. Stiebing believes this was because he revered his mother's gods (285). Nabonidus claims in the clay cuneiform tablets found in the tower to have rebuilt it on the same foundations and using the same mortar and bricks. Ultimately it must have deteriorated after the Persian defeat by Cyrus in 539 BC.

Construction of Tower of Babylon (ca 600 BC)

While the biblical account of this great structure in Genesis 11 is perhaps legendary, scholars have come to view the "Tower of Babel" mentioned in the text as the ziggurat of the temple of Marduk in Babylon (known as Etemenanki). Expressing the scholarly consensus, Foster and Foster write, "In the Bible, the ziggurat of the temple of Marduk at Babylon was transmuted into the Tower of Babel, emblematic of the vain desire of the human race to rival God" (Foster and Foster 64). It was probably the most magnificent ziggurat of all, eclipsing its far earlier model at Ur. It is not unlikely that, since Babylon is only 700-800 miles from Jerusalem, travelers could have brought news of this building to the Jewish center. "Babel" apparently meant "the gates of Heaven" in Babylonian, which explains the Hebrew use of the word.

Scholars are uncertain who built the Esagila (temple of Marduk), but they are certain that Esarhaddon and Asshurbanipal refurbished it repeatedly, along with its ziggurat, Etemenanki. Any notion that the Tower is an example of the failure of project management by communication breakdowns stems from the biblical text. There is evidence that the structure was finished, but this idea of project mismanagement is important in signaling the length the project took to come to fruition (over the reign of many kings), its constant rebuilding and renovation, and the labor force used to build it, which would have consisted largely of conquered slaves from various lands who would have spoken different languages. Thus, the project would have been difficult in terms of the project managers' ability to communicate with those who did not speak Babylonian but were the actual labor force. Confusion on the work site is imaginable.

It was not until around 600 BC that this ziggurat received its definitive and most impressive expression -- growing to either seven or eight tiers with a base and a height of 300 square feet -- under the building program of Nebuchadrezzar. This powerful ruler sponsored a total architectural overhaul of the city's main structures, rebuilding the shrine and ziggurat of Marduk, constructing palaces, creating the Ishtar Gate and Processional Way, and placed immense defensive walls around the city (McIntosh 109). According to McIntosh, "The Etemenanki, the precinct containing the 'Tower of Babel,' was also fortified" (McIntosh 109). Thus appears the notion of building defended religious structures. During this full-scale renovation project around 600 BCE, the tower of Babel received the form that made it a world wonder. Stiebing writes, "Nebuchadnezzar embellished the eight-tiered ziggurat (whose name means 'House of the Foundation Platform of Heaven and Earth') with decorations and covered the temple at its top with blue glazed bricks" (Stiebing 283). This is consistent with McIntosh's finding that the Ziggurat of Marduk, or the Tower of Babel, was probably painted. She writes, "Ziggurats were apparently painted; the traditional colors for seven-tiered examples like those at Babylon and Dur-Sharrukin were, from the bottom up, white, black, red, blue, orange, silver, and gold" (McIntosh 202).

McIntosh briefly summarizes the history of its modern rediscovery:

Between 1899 and 1914, Koldewey surveyed the whole city of Babylon, establishing its plan, and excavated most of its principal buildings, including palaces, the massive walls surrounding the whole city, and the sacred precinct of the city's patron deity, Marduk. Here he located the ziggurat that was probably the Tower of Babel; unfortunately, after the departure of the German team the local people totally destroyed it, using its bricks for construction. (McIntosh 33)

Obviously this loss was one reason why the structure is less amenable to study. Nonetheless, the Babylonians were defeated eventually by the Assyrians, their great fortified city sacked, their leaders executed, and their people enslaved. Nothing is known of what happened to the Tower of Babylon until the interest of Hellenistic Greeks in ancient Mesopotamian relics. Apparently enamored with the ziggurat of Marduk, Alexander the Great initiated its reconstruction but work ceased when he died.

Construction of Hanging Gardens of Babylon (ca 600 BC)

As legendary as the Tower of Babylon, the Hanging Gardens have never been satisfactorily located. Koldewey thought he had located them, but most dispute his claim since the place he designated was too far from a river source. The Hanging Gardens of Babylon were reputed to have been built by Nebuchadrezzar for his Median queen, Amyitis. The earliest surviving mention of this is around 270 BCE in a Babylonian author named Berossus. According to McIntosh, "He wrote of a palace built by Nebuchadrezzar II in just fifteen days, in which a 'hanging garden' was constructed to please the king's Median queen, an edifice resembling a mountain with stone terraces planted with trees" (McIntosh 311). A further royal inscription described his palace as a high stone mountain, but no garden is mentioned. Later Greek descriptions fill out some details, indicating that the gardens were a tiered structure built on stone foundations with brickwork above and layers of reeds and bitumen. All these were standard features of Mesopotamian architecture, as in the ziggurats. If accurate, this points to a building with thick lower walls, foundations, and vaulted chambers to support a tiered superstructure. In addition, it would have to be close to a water source (the Euphrates River) from which water was raised. If Snell's analysis of the social conditions of Babylonian society is correct, then like the ziggurats the labor on the hanging gardens would have been done by peasants and slaves (Snell chapters 3-4). As with all ancient buildings, the designers are unknown, unless the king himself functioned in this capacity.

What makes the Hanging Gardens significant is in their use of irrigation to create an artificial environment that mimicked natural habitat. Nebuchadrezzar was not the first to make artificial pleasure gardens in a palace precinct that were stocked with exotic plants and animals (like a modern botanical garden). Foster and Foster attribute the founding of this tradition to Sennacherib. They write, "Many rulers of ancient Iraq and elsewhere had kept foreign plants and animals, but Sennacherib may have been the first to construct authentic habitats for them" (Foster and Foster 121). Construction of this type depended on a technology for capturing, raising, and distributing water.

How was this possible architecturally? Greek descriptions mention a secret architectural mechanism embedded in the gardens for providing water to all the plants. McIntosh writes, "A hidden mechanism fed the terraces with water to support the trees, and there were pavilions among the vegetation" (McIntosh 311). Foster and Foster mention that the Assyrian king Sennacherib "seems to have invented the water-raising machine we call the Archimedes screw" (Foster and Foster 121). This device is described in an inscription that dates well before Archimedes. For irrigation, they already used a device called a shaduf, which lifted water from canals for irrigation or into reservoirs. In the Hanging Gardens, water was not supplied by gardeners, since as McIntosh reasons, "To supply the hanging gardens with water in this way would have required an army of gardeners and, more importantly, would have been visible" (McIntosh 311). While the exact mechanism for supplying water to the gardens is inexactly known, the builders utilized some system of water-raising that was ingeniously hidden. It is known that Mesopotamian architects were experts in irrigation, having founded the first agrarian-based societies (Snell 36). The engineering technology was developed out of their expertise in irrigation systems. The tiered Hanging Gardens is the first known building that was constructed with such an engineered system for water-lifting.

Some have suggested they were a roof garden on top of a royal palace. Foster and Foster educe two recent studies that suggest other versions of what the Hanging Gardens may have looked like. The first vision, based on a garden relief from the Nineveh palace of Assurbanipal (668-627 B.C.E.), describes the structure as cascading from elaborate colonnades and terraces along the Khosr River banks. The second indicates a garden that is viewed from above. They write, "The other proposes that these were the world's first carpet gardens, intended to be admired from above, so that the flowers and shrubs appear wondrously suspended, a living, dazzling display of color and pattern" (Foster and Foster 122).

This shows the recent scholarly shift in understanding the origin and location of the gardens from Babylon to Nineveh. McIntosh gives the following evidence (McIntosh 312). The fact that Herodotus, who may have visited Babylon in the 5th century BCE, failed to mention them, combined with their hard to identify location has pointed scholars in the direction of Nineveh. The palace walls at Nineveh depict gardens. Ashurbanipal and queen picnic among lush verdure. Other reliefs show terraced treed slopes and pavilions. Sennacherib knew hydraulic engineering and was interested in artificial landscapes like natural reserves with swamp for water management with birds and animals. Aqueducts and dams brought water to Nineveh from Zagros and watered whole city and orchards and parks and gardens and spice trees in it, including a royal park. The weight of this evidence suggests that the Hanging Gardens are better placed in Nineveh, where later the story of their magnificence was transferred to Babylon.

Construction of the Giza Pyramid

Pyramids are principally royal tombs, not temple structures like the ziggurats. They exhibit different properties as a result. Their slope is more extreme, they have no platforms, and at the top they taper to a point. Any ritual would have been performed inside, not outside in open space due to the lack of upper shrine or architectural climax. Furthermore, they were not equipped with stairs or ramps for climbing as were the ziggurats.

The land was first surveyed with measuring ropes of palm or flax fiber, and then leveled. The walls, piers, and roofs of the Giza pyramid are made of Aswan red granite and its passages and outer casing of polished Turah limestone. In a microgravimetric study of the pyramid's density, two French companies found that "the pyramid's macrostructure consists of 34 major 'blocks' with a low-density block near the top, and blocks of heterogeneous density below" (Lehner 67). Lehner writes, "The Great Pyramid contains about 2,300,000 blocks of stone, often said to weigh on average c. 2.5 tons" (Lehner 108). It is uncertain whether the inner core is well-cut or uniform, and the stones get smaller towards for increased precision. At the base, some casing stones weigh 15 tons, while the granite beams above the stress-relieved King's Chamber weight 50 to 80 tons. An innovative arrangement was used above this chamber to distribute weight and stress by means of cantilevered stones forming a pent roof. According to Lehner, "Large quantities of gypsum mortar were poured into the often wide interstices between the core stones" (Lehner 109).

Built over three generations, there are no extant Egyptian records giving the methods used. It is still unclear whether the core was erected first with the use of earth ramps, or whether the casing stones were placed and beveled to the incline angle and then the frame filled with core blocks (Kostof 77). The stones were apparently quarried elsewhere with intensive labor that did not involve iron tools. Nuttgens writes, "They never learned to harden copper, so, although they had both saws and drills of copper, the tough granite of Aswan had to be split from the rock face, first by hammering vertical trenches into the rock with balls or hammers of a hard rock called dolorite and then by driving in wedges either of metal or of wood that was soaked in water until it expanded" (Nuttgens 33). Lehner adds to this: "With only tools of stone, wood or copper at their disposal, the ancient quarrymen had to use large wooden levers to detach blocks, and needed considerably more room to manoeuvre" (Lehner 206). To cut the granite, they probably used copper saws to guide gypsum and sand which had an abrasive effect (Lehner 215). Then they smoothed the casing with chisels and pounded out blocks with deep channels.

The stones were loaded onto barges for transport down the Nile, sometimes hundreds of miles. "R. Engelbach proposed that Hatshepsut's great granite obelisks were loaded and unloaded from the large barges . . . By means of an earthen embankment, which would have been built up around the barge as high as the deck" (Lehner 202). Alternatively, the barge was brought into a narrow canal and cedar beams were placed beneath the load between supports as the barge slipped out, leaving the stones. How were the stones transported over land? Scholars believe it was through the manual pulling of sledges (by humans or cattle) across timber-baulked hauling tracks lubricated with mud or water. This process is depicted on tomb scenes (Lehner 203).

The greatest mystery is how such a massive structure was constructed without the use of cranes and pulleys. How did they move and life such huge stones? Nuttgens says, "But the Egyptians did not have cranes -- possibly they did not even know the principle of the pulley, although they certainly used the lever" (Nuttgens 33). Lehner's NOVA experiments show that levering and tumbling with wooden poles was possible, but only for side movements, final adjustments, and setting uppermost stones. He says that the most likely method was "some system involving a ramp or ramps" (Lehner 209). The ramps could have been either straight on, perpendicular, spiral at corners, or zigzag up one face. There is no scholarly consensus on the matter. Nuttgens believes they laid the stones level and worked from the earth of mud-brick ramps, building them up as they proceeded (Nuttgens 34). But the challenge is almost incomprehensible due to the steep gradient of the slope that would make building a ramp itself an incredible feat. The fact that the outside face was often staggered rather than flush, compounded by the reduced working space, suggests that for high levels the outer slope was cut into the blocks before they were laid (Lehner 123).

What is certain is the huge labor force needed. The Pharoahs employed a regular workforce of skilled masons and craftsmen that was "undoubtedly occupied full-time during the span of construction," probably augmented with peasant labor when flooding prevented farming from May to September (Kostof 77). Kostof says "we should refrain from seeing the pyramids as the repressive fruit of slave labor" (Kostof 77). Lehner estimates a workforce of 25,000 of stone haulers and setters on shift every three months (Lehner 224). The workshops would have used massive amounts of fuel from the countryside for forging copper tools, slaking gypsum to make mortar, and baking bread for workers.

As to the idea behind the construction, the pyramid was a tomb for the king's transport to the otherworld. Entrances were concealed and interior mazes built to protect royal wealth and ensure safe translation into immortality. There is an obvious cosmological focus as well. The shafts in the king's tomb were aligned with the three stars of Orion. The geometry was precise, with perfect squares and sides of equilateral triangles. The abstractions had much to do with sun worship

Construction of the Roman Colosseum (75-81 CE)

The Colosseum in Rome, which is the largest of the Roman amphitheaters, is situated on the site of the former lake of Nero's Golden Palace. According to Bonde, Maines, and Richards, its foundation is a twelve meter deep ring of concrete and stone blocks (Bonde, Maines, and Richards 29). It is 188 meters long by 156 meters wide. It has eighty arches around it with two annular corridors at ground level and three storeys of stairs to different levels of seats. Encompassed in it are numerous subterranean chambers and passages. Concerning its material, Ward-Perkins says, "The main load-bearing skeleton was of dressed stone masonry throughout, travertine externally and tufa internally; concrete was limited to the vaults and upper internal walls and, to minimize the thrust of the uppermost tier of seating against the unsupported outer wall of the attic, the seating was of timber" (Ward-Perkins 94). The joining surfaces of stone were cut and mortared. In lieu of mortar, iron cramps and dowels were used to fasten blocks together. The original structure was covered with a veneer of travertine, and its perimeter wall was made of marble ashlar with brick facings of pozzolan concrete-filled (Bond, Mark and Robison 82).

There is little, if any, controversy over the dating of the construction. The Colosseum was begun by Vespasian in 75 CE and virtually completed by Titus in 81 CE, by which time five levels had been finished. The second concentric passageway allowed the additional banks of seats above, in turn making a third order of arches necessary in the outer wall. Bonde, Mark, and Robison say, "Domitian added a fourth story in A.D. 81-82, but all trace of the upper seats has been lost, suggesting that they were constructed of wood" (Bonde, Mark, and Robison 82). These authors mention a canvas awning that was stretched over the roof and attached to stone corbels.

There are different views as to how the work proceeded. Scholars have tried to understand how quickly the building was erected. Ward-Perkins thinks the work place was divided for simultaneous construction. He writes, "To speed construction the work was broken down into four quadrants, each further subdivided by materials into what must have been a very carefully scheduled working program" (Ward-Perkins 94). Bonde, Mark, and Robison are likewise certain of unconventional methods and make this proposal:

Rather, it appears that construction began with the raising of the outer travertine walls up to the top of the first order, together with the two concentric walls behind them. Piers were then constructed up to the point of the vaults, leaving only a concealed springing for the alter vault construction. Finally, brick arches were built to support the sloping barrel vaults, which in turn supported the banks of seats. Virtually the entire skeleton of the Colosseum could in this way have been erected in a short time, permitting large gangs of skilled and unskilled workers to fill in the spaces between the piers later on. (Bonde, Mark, and Robison 82)

There is no way it was completed so quickly without massive amounts of labor.

After careful study, Taylor presents a plausible explanation for sequential process in building the Colosseum. Speaking of the legend of 15,000 prisoners from the Jewish war helping, he says, "While they might have joined the slave forces transporting materials and pulling ropes, they could not have augmented the highly skilled and specialized workforce of craftsmen working these local materials in local fashion" (Taylor 137). He says that more than a dozen guilds of building specialists are attested in the construction of the Colosseum. His view is that the logistics were worked out beforehand, with efficient management of slaves and free workers, bricks already cured and fired, and quicklime slaked months in advance. He describes how during construction "legions of artisans were shaping the thousands of stones to be fitted, how arches "would be laid out on templates, blocks carefully measured, sawed, and chiseled according to detailed specifications either of the architects or of a master stonemason working from plan and elevation diagrams" (Taylor 138). The final dressing of stones was done at the end. His study indicates a complex overlapping of tasks and stresses the material conditions that helped the flow of work through chambers and around material. He opts to see the crews working circumferentially, rather than vertically, which was more efficient in terms of the use of stone-hoisting cranes and ensured work was being done on different parts simultaneously.

The Colosseum had a drainage and water supply network. According to Taylor, "The downspouts, gutters, and water-supply pipes numbered in the hundreds, and each was positioned roughly according to its estimated capacity," veined into walls, piers and concrete foundations (Taylor 143). What is most important, however, is that the Romans used cranes to lever stone blocks. The details are immense, but Taylor's book is crucial for understanding the Roman use of shear or A-frame cranes to work in confined spaces around the building before they were situated on higher levels. Many cranes operated simultaneously and on multiple levels. He gives important details about the load-capacity, the tilt, the reach, and the maneuverability of cranes during construction. Men and animals pulled the ropes. Scaffolding and formwork was only brought in for vaulting. He writes, "At this stage the cranes would be removed and timber formwork and scaffolding introduced" (Taylor 156).

Construction of Caesar's Rhine Bridge (55 BC)

"The earliest recorded major bridge is a timber bridge built by the Chaldean king Nabopolassar over the Euphrates River at Babylon" (O'Connor 139). The Romans likewise built timber bridges, though what remains of their architectural prowess are the great stone bridges. Romans produced the first true bridge engineers due to the high priority that they were to the maintenance of empire (in terms of efficiency, communications, and transport). Caesar's Rhine Bridge is perhaps a legendary example of a wooden bridge built in service of empire.

Bennett says that Roman timber bridges were preserved by soaking wood in oil and resin as protection against dry rot, and coating them with alum for fireproofing (Bennett 14). In his view, they knew the difference between hard and soft woods. For example, they knew that oak was the best for substructure work in the ground, alder was best for piles in water, and fir, cypress, and cedar were best for any superstructure. It is unlikely that these measures were taken in building Caesar's Rhine Bridge, which was meant only as a temporary structure.

Caesar himself describes the bridge construction (Gallic War 4.17). Its method involved pile driving thick timber piles, fastened two feet apart, obliquely (in direction of current) into the river at right angles to the bank. Forty feet downriver, the same was done. These piles were joined by two foot wide beams fitted into the spaces between the two piles of the pair. A diagonal tie was arranged between pile pairs. The upper pair was kept at right distance from the lower pair by iron braces. For protection against floating attack, an additional pile was driven in front of each pair. Then planks were laid over the structure, allowing passage over the river.

The location of this bridge is unknown, but the most probable guess is Coblenz. The equipment used is unknown as well. O'Connor says:

If Caesar's bridge was at Coblenz, then its length would have been at least 260m. Assuming a pier spacing of 10m, the number of piers would have been about twenty-six. To complete the bridge in ten days, Caesar would have had to average almost three spans a day. . . . Equipment would have been his major problem -- in particular for lifting and pile driving. His description implies that is piles were driven in pairs; that the two piles were attached together 2 feet apart and then driven into the river bed. (O'Connor 140)

Most remarkable was that the army could make six pile pairs a day, and that the whole bridge was completed in ten days. Caesar's army crossed over the Rhine into "barbarian" territory (Gaul). Then they recrossed eighteen days later and destroyed the bridge. The purpose of the whole exercise seems to have been to demonstrate the speed of the Roman army, perhaps, to awe the tribes, to show symbolically that Caesar was victorious over their river god, and to use this technical achievement for political means (to hurt the barbarians morale). Caesar routinely built such bridges when going out with his army (e.g., later across Loire and Saone rivers).

Construction of Aqueduct Pont du Gard (15 BC -- 14 AD)

The Romans built aqueducts mainly to provide towns with bath water. Hodge says, "For one thing, aqueducts were usually built to supply baths, not drinking water, though (once n place) they were used for that too. Most Roman towns only acquired an aqueduct well on in their history, and before it arrived relied quite happily on wells" (Hodge 128). These stone and concrete structures were not monuments of progress to those from whom water was taken to provide baths in Roman military camps. About ninety percent of the aqueduct was underground and out of sight using tunnels and basins.

Most likely it was Agrippa who ordered and financed the construction of the aqueduct of Nemausus (Nimes) around 20 or 19 BCE, the apex of which is the Pont du Gard across the Gardon River. This dating is based on the dating of the city walls. According to Hauck, who has done the most extensive study of this structure in English:

No one knows how, exactly, the project got underway, or how long it took. No one knows how much it cost, or how it was financed. No one knows how many thousands of people were employed, or whence they came. No one knows who was responsible for what, who was in general charge of the project. Furthermore, it is unlikely that these fundamental questions will ever be definitively answered. (Hauck 2)

He believes it was built quickly, taking less than two years.

The Romans (e.g., Pliny) use various terms to talk about those who managed construction of aqueducts, such as architectus or mechanikos (master-builder or architect), aquilex (conduit master to find water sources), and librator (leveler or surveyor). Although there was no separate engineering corps, O'Connor says that the army provided the major bulk of technical leadership in bridge construction and the provision of skilled labor, while higher official master-builders were predominantly civilians (O'Connor 42). The soldiers were the brawn for quarrying and laying stone, which was good for discipline and cost effectiveness. The Legion was responsible for building aqueducts and bridges, but some were immunes, like priests, surveyors, master builders, craftsmen, carpenters, hydraulic engineers, and stonemasons -- these were the military class that was "exempt from the arbitrary control of the centurion" (O'Connor 42). The final source of labor was slaves, who were not cheap, oppressed, or unskilled.

Hauck expertly describes the organization of the building process. The land was first surveyed (in a scouting-like trip) using sophisticated leveling instruments (chorobates, groma, dioptra) (Hauck 43-44). After the mapping and design by the aquilex, they built roads for bringing in stone, and turned to the