History of energy in Ancient Rome

Summary: Rome depended for its energy on human and animal muscular strength, hydropower, wood and charcoal (biomass), and wind energy. Romans refined many of the technologies of the Greeks, notably hydropower and sanitation.

Ancient Rome’s technological superiority was based on its progressive engineering and led to the construction of roads, aqueducts, thermae (large bathing facilities with heated water), theaters, and arenas. Even though some technological designs were inherited from the Greeks, the Romans added many impressive innovations. In ancient Rome, five different energy sources were available: human muscular strength, animal power, hydropower, wood and charcoal, and wind energy. Many of Rome’s advancements, especially regarding the use of hydropower and sanitation (including pertinent logistics), were lost in the Middle Ages and not revived or reinvented until the 19th century.

After more than a millennium, the ruins of formidable monuments, such as the Pont du Gard, the Colosseum, and the Pantheon, remain in Italy and across the Mediterranean region as testaments to Roman engineering and culture. There are two major sources for what is known today about Roman technology: Vitruvius’s De architectura (On Architecture, written around 15 b.c.e.), books 8, 9, and 10, and Pliny the Elder’s Naturalis Historia (published a century later, around 77–79 c.e.).

Using the primary energy source at that time, many devices were powered by human muscle labor; these included tools such as the potter’s wheel and building cranes, whereby heavy objects and weights could be erected by means of treadwheels. Trading vessels used wind to sail, but warships that had to be maneuvered independent of wind were driven by oarsmen. Wind power was used only in shipping; there was no other technological use. Within cities, because of narrow streets, humans carried loads, including sedans bearing wealthy citizens. In agriculture and for transportation, the power and traction of oxen, donkeys, and mules were used. Horses were used mainly in the military and the circus. Rotary motion was used for the first time in grain mills. One example of animal labor being substituted for human power was in the Pompeian mill.

Concrete

The Romans developed several innovations in construction engineering and architecture. One famous example is the Pantheon in Rome, which was the first big building with a dome, an arched roof not supported by pillars. Most of these construction innovations were based on the introduction of concrete, opening the door for innovative architectural designs, as well as paved roads. Concrete had been invented in the late 3rd century b.c.e. based on a volcanic ash called pozzolana. It was not until the 1st century, however, that concrete replaced marble as the main Roman building material. Rome’s power was especially strengthened by its empire-wide paved roads. Originally built for military use, to deploy Roman legions efficiently, these roads soon became economically important for trading. A well-maintained system of way stations offered refreshments to travelers, often combined with the possibility of horse relays enabling couriers to travel up to 500 miles in 24 hours.

Waterwheels and Mills

The water mill, invented apparently in the Hellenistic era, was one of the earliest mechanical constructions to use natural forces to replace human muscular labor and as such holds a special place in history of technology. During the subsequent Roman era, the use of hydropower was diversified and different types of water mills were invented, using variants of both the vertical and the horizontal waterwheel. Apart from its main use in grinding flour, hydropower was also applied to pounding grain, crushing ore, and sawing timber, marble blocks, and stones.

Vitruvius describes both simple scoop wheels and the more extensive construction of the water mills, which used geared wheels to transfer the kinetic energy onto a millstone. He also writes about lifting machines, such as the reverse overshot waterwheel, with its endless chain of buckets, and a device known today as Archimedes’s screw, widely used for raising water to irrigate fields and to dewater mines. Romans also used so-called noria (bucket wheels), primarily combined with aqueducts. They are reported to have had diameters up to 98 feet (30 meters). Even in literature they are mentioned. Around 65 b.c.e., the Roman author Lucretius refers in the poem “About the Nature of the Universe” to a bucket machine powered by a waterwheel. Grain mills were a widespread rural phenomenon. Palladius advised landholders to build water mills, to mill grain independent of human or animal labor.

Numerous archaeological finds of Roman sites throughout Europe show that the water-mill technology was well developed and widespread by the 1st century c.e. When old mines at Rio Tinto in Spain and Dolaucothi in Wales were reopened in mining attempts, remains of waterwheels used for lifting water have been found. Originally, they were linked together in a vertical sequence capable of raising water at least 96 feet above the water table. Each wheel required a miner to drive it, treading the device on top of the wheel by using cleats on the outer edge.

In the late Roman Empire, some adaptations and advancements occurred. After destruction of the mills at Janiculum by a Gothic attack in 537 c.e., General Belisar ordered the installation of water mills on ships, powered by the flow of the Tiber River. Ship mills became a common source of water supply to cities in the Middle Ages and were in use until the 19th century. The mechanical sawing of marble was not possible with the rotary motion of water mills. To achieve a seesaw motion, a transmission, incorporating a crankshaft and connecting rod, was required. This was first used at the Hierapolis sawmill in the late 3rd century c.e. Similar mechanisms were found in Ephesus (Turkey) and Gerasa (Jordan); they date to the 6th century c.e. In the 4th century, Saint Gregory of Nyssa has written about marble-sawing mills in Anatolia. These sources indicate a broad use of such mills in the late Roman Empire.

Force Pump

The inventor and mathematicianCtesibius of Alexandria (who flourished around 285–222 b.c.e.) is credited with the invention of the force pump, which Vitruvius describes as built from bronze with valves. Force pumps allow a head of water to be formed above the machine. The device also was described by Hero of Alexandria (c. 10–70 c.e.) in his Pneumatica. The machine is operated by hand in moving a lever up and down. He mentions its use for supplying fountains above a reservoir, although a more mundane use might be as a simple fire engine.

Aqueducts

The first Roman aqueduct, Aqua Appia, was built in 312 b.c.e. during the time of the Roman Republic. Aqueducts were channels, built to convey water, as the Latin root of the term indicates: aqua (water) and ducere (to lead). In modern engineering, the term is used for any system of pipes, ditches, canals, tunnels, and other structures for moving water over long distances. In a more restricted use, the term aqueduct applies to any bridge or viaduct that carries water across a depression.

The Romans constructed numerous aqueducts all over the territory of the former empire to supply water to cities, mining sites, and agricultural fields. Often, arches were built in conjunction with aqueducts, but they should not be confused with the aqueduct itself. Arches were constructed, sometimes even on several tiers, because they were known to be very stable structures. Their purpose was to maintain the pitch of the aqueduct over irregular terrain. Even huge navigable aqueducts, used as transport links for boats or ships, are known.

Water distribution, including the quality of the water and its rate of discharge, depended on its height as it entered a city, among other factors. Accordingly, poor-quality water was channeled to be used for irrigation of crops, watering of gardens, or flushing; intermediate-quality water was used for baths and fountains; and only the best water was reserved for drinking and other potable uses.

Some aqueducts were used to drive water mills by linking them in series down the side of a hill. The mills of Barbegal at Arles, where one aqueduct fed 16 mills, and Janiculum, at the terminus of Aqua Traiana (the highest aqueduct of Rome), are two of the most impressive examples. Arrangements like these fulfilled diverse functions, not only carrying water to the city but also working as grain mills and stamp mills to forge iron.

Vitruvius and Frontinus: Contemporary Witnesses

In the 1st century b.c.e., Vitruvius wrote De architectura, the oldest known completely preserved treatise on architecture, in 10 books. In book 8, Vitruvius describes in detail the methods of constructing aqueducts. Besides providing structural directions, he specifies the tests needed to ensure that the water is potable. Vitruvius knew about the toxicity of lead and warned against its use in pipes, recommending that either masonry channels or clay pipes be used instead.

It is assumed that Julius Sextus Frontinus, a general who was appointed curator aquarum (water commissioner) in 95 c.e. by the emperor Nerva, learned from Vitruvius’s book. Frontinus made a meticulous survey of the intake and supply of water of each line and gave detailed statistics two years later in the two-book report De aquaeductu (on aqueducts), also known as De aquis or De aqueductibus urbis Romae (on the aqueducts of the city of Rome). The work describes all nine of the aqueducts of Rome that existed in his time—the Aqua Appia, Anio Verus, Aqua Marcia, Aqua Tepula, Aqua Julia, Aqua Virgo, Aqua Alsientina, Aqua Claudia, and Anio Novus—reporting the sizes of the channels, their discharge rates, and the quality of water delivered by each. Frontinus also covered the laws relating to their use and maintenance.

Starting his investigation, Frontinus first prepared maps of the system to assess their condition before undertaking their maintenance. Most important for his work, he unveiled a discrepancy between the intake and the supply of water caused by illegal division of the supply. Farmers and tradesmen had inserted unapproved pipes into the channels to divert water for their use. Upon this report, lead pipe inscriptions providing the name of the owner were introduced to prevent water theft. Although Rome was later fed by 11 aqueducts, there is no other report like that of Frontinus.

Surveying

Roman aqueducts were highly sophisticated constructions that required accurate surveying to ensure a regular and smooth flow of water. It was again Vitruvius who provided posterity with descriptions of surveying instruments used in the construction of Roman aqueducts. The groma, the main instrument used in Roman surveying, was a vertical pole (ferramento) that supported a bracket (rostrum) to which was mounted crosspieces (stelletta) at right angles; from each end of the stelletta a weighted plumb line hanged vertically. The groma was used to survey straight lines and right angles, thence squares or rectangles. The instrument that is the forerunner of the theodolite was known as the dioptra and was used to measure vertical angles. The chorobates was used to level terrain before construction. It was a wooden frame, supported by four legs, holding a flat board fitted with a water level and wooden arches to support the vaults. Vitruvius also describes the hodometer, principally a tool for automatically measuring distances along roads, essential for developing accurate itineraria, or maps in the form of lists of destinations, such as the Peutinger table.

Because aqueducts are entirely powered by gravity, the most complex part of their construction involves estimating the right gradient, because if the gradient is not correct, the aqueduct will either overflow or clot. The volume of water actually transported depended on the catchment hydrology (rainfall, absorption, and runoff) and on the quality of maintenance. Vitruvius suggests a low gradient of not less than 1 in 4,800 for the channel, presumably to prevent damage to the structure. This use of value has been confirmed by measurements of surviving masonry aqueducts. Additionally, there were industrial sites—for example, gold mines, as preserved in Dolaucothi in Wales and Las Medulas in northern Spain. The average gradient of the 7-mile-long structure at Dolaucothi is about 1:700, that is much higher than those of the masonry aqueducts.

Whenever valleys deeper than 165 feet (50 meters) had to be crossed, gravity-pressurized pipelines called inverted siphons, as described by Vitruvius, and so-called venter bridges were used to force water to flow uphill. Vitruvius knew about the problems of blowouts, resulting from spots where the pressures were greatest. Today, hydraulic engineers use similar techniques to enable sewers and water pipes to cross depressions. It is interesting to note that the maximum capacity of ancient Rome’s aqueducts exceeded the modern water supply of the Indian city of Bangalore, which has a population of 6 million.

City of Rome

In the 1st century c.e., the city of Rome had a large population of 1 million people. In order to meet their massive water needs, the city of Rome was supplied with 11 aqueducts. Their combined length was about 260 miles (420 kilometers) with a capacity of about 1 million liters (almost 300 million gallons) of water supply daily from the Apennine Mountains to the city. While the aboveground remains are supported by arches, the aqueducts were built mainly underground, in order to keep the water clean and protect the aqueducts from enemy attacks.

Freshwater reservoirs in the form of cisterns were commonly set up at the termini of aqueducts and their branch lines, supplying urban households, agricultural estates, imperial palaces, baths, and bases of the Roman navy.

Wastewater was channeled into the main sewers, which led into the Cloaca Maxima and finally the Tiber River. The continuous supply of running water helped to remove wastes and keep the sewers clear of obstructions.

Example: Pont du Gard

The Pont du Gard, today one of France’s most popular tourist attractions, is an ancient Roman aqueduct bridge crossing the Gard River at Vers-Pont-du-Gard. Constructed in the 1st century c.e., it was part of a 31-mile-long (50-kilometer-long) aqueduct that runs between a spring close to Ucetia (now Uzès) and a delivery tank, or castellum divisorum, in Nemausus (Nîmes). At the time, it supplied an estimated 44 million gallons (200 million liters) of water per day, which took almost 27 hours to flow from the source to the city. Although the straight-line distance is only about 12 miles (20 kilometers), the aqueduct takes a winding route to avoid the Garrigue Hills (southern Massif Central) above Nîmes.

Standing 160 feet (48.8 meters) high and 899 feet (274 meters) long, it is the highest of all Roman aqueduct bridges, built on three levels in rows of arches. Its width ranges from 30 feet (9 meters) at the bottom to 9.8 feet (3 meters) at the top. The major part of it was constructed underground by digging a trench in which a stone channel was built and enclosed by an arched roof of stone slabs, which was then covered with earth. Some sections of the channel are tunneled through solid rock. The remaining structure had to be carried on the surface, either on a wall or on arched bridges. The function of the Pont du Gard as a toll bridge ensured its survival in the Middle Ages. Local lords and bishops were for centuries responsible for its upkeep in exchange for the right to levy tolls on travelers using it to cross the river. Repeatedly, stones from the aqueduct were stolen for use elsewhere; nevertheless, the Pont du Gard today is by far the best-preserved section of the entire aqueduct.

The aqueduct descends in height by only 56 feet (17 meters) over its entire length. Its average gradient of 1:3,000 is sufficient to sustain a steady flow of water and indicative of the great precision that Roman engineers were able to achieve using only simple technology. The Pont du Gard itself descends 2.5 centimeters (barely an inch) across a distance of 1,496 feet (456 meters), a gradient of 1:18,241. Since 1985, it is has been listed as a World Heritage site by the United Nations Educational, Scientific and Cultural Organization (UNESCO).

Industrial Aqueducts: Mining and Hushing

Numerous aqueducts supplied water to industrial sites, such as gold mines. They usually differed from masonry structures in consisting of an open channel dug into the ground with a clay coating and sometimes timbering to prevent excessive loss of water. They dug channels, called leats, were much more expensive than the masonry structures.

Large quantities of water were used for prospecting ore bodies by a method later known as hushing. Therefore, the Romans stored a large volume of water in a reservoir immediately above the area to be mined; the water was then quickly released. This flush of water removed overburdened and exposed bedrock. Additionally, the Romans set fires against the hard rock face to weaken the rock and make removal of the ore much easier. Water was also used to work simple machines, such as ore-crushing hammers and waterwheels. In medieval times, these methods of mining were replaced by the use of explosives.

The remains at Las Medulas, now a UNESCO World Heritage site, show badlands on a gigantic scale due to hydraulic mining of the rich alluvial gold deposits. There were at least seven major leats at Las Medulas, and at least five at Dolaucothi feeding water from local rivers direct to the mine head. At Dolaucothi, the only known Roman gold mine in Britain, holding reservoirs as well as hushing tanks were used; sluice gates controlled flow, and drop chutes diverted supplies. In his Naturalis historia (1st century c.e.; Natural History), Pliny the Elder, at that time procurator in Hispania Tarraconensis (the region occupied by modern Spain’s central plateau, Andalusia, and northern Mediterranean coast), describes Roman gold-mining operations.

After the fall of the Roman Empire, the maintenance system collapsed too. Following the decline of a functioning water supply, the population was drastically reduced as well, reaching as few as 30,000 in the medieval era. The first of the ancient aqueducts to be restored in renascent Rome was the Aqua Vergine, in 1453 under Pope Nicholas V.

On the other hand, many aqueducts elsewhere in the empire continued in use, including the one at Segovia in Spain, a structure that shows advances in comparison with the Pont du Gard (the use of fewer arches of greater height and so greater economy in the use of the raw materials). Remains of Roman aqueducts are also to be found in Bulgaria, Croatia, France, Germany, Greece, Italy, Israel, Lebanon, the Republic of Macedonia, Spain, Tunisia, Turkey, and the United Kingdom, reminding us centuries later of the Roman Empire’s huge expanse and sophisticated harnessing of energy.

Sanitation and Plumbing

The Romans boasted major advancements in sanitation, achieved through Etruscan engineers and large amounts of semiforced labor from the poorer classes of Roman citizens. The very first sewers of ancient Rome were built between 800 and 735 b.c.e., primarily to drain marshes and storm runoff. The sewage system as a whole did not develop until the installation of the Cloaca Maxima (literally, “greatest sewer”), an open channel that was later covered by stones, one of the best-known sanitation artifacts from the ancient world. Most sources believe it was initially built during the reign of the three Etruscan kings. The Cloaca Maxima was thought to be presided over by the goddess Cloacina.

Over time, the Romans expanded the network of sewers. In 33 b.c.e., under the emperor Augustus, they enclosed the Cloaca Maxima, creating a large tunnel beneath Rome. Public bath wastewater was used to flush the latrines.

The Cloaca Maxima was well maintained throughout the life of the Roman Empire and even today drains rainwater and debris from below the ancient Forum, Velabrum, and Forum Boarium. In more recent times, the remaining passages have been connected to the modern-day sewage system, mainly to cope with problems of backwash from the river. The Romans were the first to seal pipes in concrete to resist the high water pressures developed in siphons and elsewhere. Beginning around the 5th century b.c.e., Romans employed special city officials, called aediles, to supervise the sanitary systems; they were responsible for maintaining the systems, cleaning and paving streets, preventing foul smells, and monitoring brothels, taverns, and baths. The efficiency of the Roman sewage system was praised by Pliny the Elder in his Natural History. The Greek writer Strabo (c. 64/63 b.c.e.–24 c.e.), in his Geographica (c. 23 c.e.; Geography), notes that the sewers had room in some places for hay wagons to drive through them.

Nonetheless, most private homes in early Rome were not connected to the sewers, and people either used pots that they emptied into the sewer or visited public latrines. Eventually, frequent street cleaning with aqueduct water washed most human wastes into the sewers. Around 100 c.e., direct connections of homes, mostly those of the wealthy citizens, to sewers began by means of terra-cotta piping. The latrines, early public restrooms, date back to the 2nd century b.c.e. and have been found in many places, such as Housesteads, a Roman fort on Hadrian’s Wall, in Pompeii, and at Herculaneum. Set up as long benches in rows with keyhole-shaped openings, they offered little privacy. (Romans used sea sponges on sticks to clean themselves after defecation.)

Romans were less sanitary than this system may make them appear. A law, called the Dejecti Effusive Actio, was put into effect to protect passersby from injury by wastes thrown out of windows. The violator had to pay damages to those his waste hit, but only if the accident occurred in the daytime.

The outfall of the Cloaca Maxima into the Tiber River is still visible today. There is a stairway going down to it next to the Basilica Julia at the Forum.

Thermae: Baths With Central Heating

Romans were particularly famous for their public baths, called thermae, which were used for both hygienic and social purposes. At that time, Romans washed their arms and legs daily and took a full bath every ninth day. Wealthy citizens built comfortable private baths. By 150 b.c.e., the first public bath had opened in Pompeii.

The invention of the first central heating system, called the hypocaust, is attributed to Lucius Sergius Orata. He gave explicit instructions how to order the architectural layout. Different rooms of the bath had water heated to different temperatures; working from the center outward, the baths were to be hot (caldarium, next to the furnace), lukewarm (tepidarium), and cold (frigidarium and natatio); all these rooms were surrounded by palaestrae (adjoining rooms for exercise) and tabernae (shops), which explains the high social popularity of public baths. Orata also advises using a type of regulator to control the heat in the hot rooms, as well as a bronze disc set into the roof under a circular aperture that could be raised or lowered by a pulley to adjust the ventilation. Such a disc was also described by Vitruvius.

The heating system was kept going by slaves. They had to fire a furnace with wood and charcoal to generate warm air. The use of coal was unusual. Hot air moved around the building through spaces or pipes under the floors and through cavities in the walls. The underfloor space was created by building the floor on piles of tile or stone.

First only men, including slaves, were supposed to use public thermae. Women had to use smaller baths, called balneae. Later, they were allowed to use the thermae too, but Emperor Hadrian prohibited simultaneous use of the baths and established different times for men and women.

In addition to the baths and private homes, in which log fires were used for cooking, fuel was needed for the smelting of ores, forging of iron, glassblowing, and producing ceramics. Regardless of the high demand, there was no sustainable forestry, resulting in extremely reduced forest stands, although already in ancient Greece some manors specialized in firewood production.

Dam Building

Roman dam construction began in the early imperial period. The dams are known for their extraordinary height, which remained unsurpassed until the late Middle Ages. Reservoir dams secured a continuous water supply for urban settlements even during the dry season, but the most common types of dam were earth- or rock-filled embankment dams and masonry gravity dams. They served for irrigation, flood control, river diversion, soil retention, or a combination of these functions.

The impermeability of Roman dams was ensured by the introduction of waterproof hydraulic mortar, especially opus caementitium, the introduction of concrete as a standard construction material. These materials also allowed bigger structures to be built, such as the Lake Homs Dam, possibly the largest water barrier to date, and the sturdy Harbaqa Dam. Both these dams were built with concrete cores.

Roman dam engineering displayed a high degree of sophistication. While hitherto dams relied solely on their heavy weight to resist the pressure of water, Roman builders were the first to realize the stabilizing effect of arches and buttresses, called weir bridges. Previously unknown dam types introduced by the Romans include arch-gravity dams, arch dams, buttress dams, and multiple-arch buttress dams.

Bibliography

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Wilson, Andrew. “Machines, Power and the Ancient Economy.” Journal of Roman Studies 92 (2002).