History Travels with Nancy Padgett: Seeing History
Ancient Rome: Technology 
The Roman Colosseum, with its dramatic arches
 The Roman Colosseum. The Colosseum opened in AD 80. The largest amphitheater of the Roman Empire, it rose 158 feet and seated 50,000 spectators. 


* What did the Romans build? What did they not build?

Roman Roads

Roman Aqueducts

* Roman Concrete and Arches:  Construction and Design

Roman Technology

I went to the Colosseum in Rome. How can it be so big? Why did the Romans want to devote their resources to large monuments? The Etruscans built on a much smaller scale. In today's technology, engineers design for The Small. We want to be connected, quickly, on ever-smaller devices.

The Romans didn't know how to think that way. They wanted to dominate, not share or learn from others. If they wanted to "be connected," it was to the gods, not to other humans. For them, there was only The Big, no matter how long it took to build.

Building Big honored the gods, always a priority for the anxious Romans.

How, in their society, did they do it? The Etruscans had built temples and presumably other public buildings. Theirs were on a much smaller scale. What did the Romans bring to the table?

What they built

The Romans radically changed the built environment of the ancient world for thousands of miles in all directions.  

The Romans built and built and built. Durable roads covered thousands of miles. Gigantic temples and basilicas dazzled the masses. Superior military installations and camps frightened the opponent.  Aqueducts, bridges, canals, and baths. Monuments, triumphal arches, columns and tombs. Large-capacity theaters and libraries. Amphitheaters and circuses. New cities, all over the Empire.

Roman technology and the expansion of Rome

They did it with applied technology. The Romans didn't know or weren't interested in science.

Roman technology was all about power, displayed very publicly.  Along the new Roman roads flowed the principles of "Roman-ness." The conquering Empire wanted the built environment to look "Roman." The "Roman look" was urban, not suburban or rural. The urban center was to be filled with towering buildings. Materials would be stone and marble, materials of wealth and durability, not of wood and tile. The Romans were saying: "Look at us: we have all the resources and we will be here forever."

About 1000 cities were created or transformed by the Romans. These new cities were built on a rigid grid. The city center of even the most modest showcased the civic buildings that Rome prized:  temples, the forum, theater, library, baths and other waterworks, sometimes an amphitheater, basilicas, and the agora (market.) 

Note what the Romans did not build: schools, hospitals, or public housing.

How could the Romans make this happen on such a large scale? Roads and aqueducts, new building designs, and new construction material were the keys.

  Arch of Constantine
Rome. The Arch of Constantine in the Roman Forum. Around 50 commemorative arches were built in Rome.

Pula (Croatia) Temple of Augustus
Pula, Croatia. Temple of Augustus. Built 2 BC.

Ephesus, Turkey. The Roman Library. Built 2nd century AD.

Roman Roads: Big Vision, Big Costs

The Romans built 55,000 miles of roads.  The Romans wanted to be everywhere. The interior of Europe and the Near East was as attractive to them as the sea coasts. Eventually the Roman Empire encompassed millions of people. 

The Purpose of a Roman road: the Military

An Empire of this size required a moveable military.  Without good roads to move its Army, the Empire would have been difficult to achieve.

A Roman general needed to launch offensives and respond quickly to a land threat. He needed infantry. The infantry needed a reliable marching surface.  The Army's logistical support, usually packed into ox-drawn heavy carts, needed deep, metaled surfaces. The unpaved tracks and simpler roads from Etruscan and Greek times crumbled or turned to mud in the rain.

How did the Romans build a road? They depended largely on laborers, both slave and military, not technology or equipment. The Romans had only a few crude engineering devices.  Since the main purpose of the roads was to hustle foot soldiers along, not for trade, the roads could be built straight.

The roads might go straight up a hill rather than contour around it. The soldiers couldn't very well complain. To go in a straight line requires only a modest surveying instrument, which in Roman times was the groma. 

As a Roman soldier trudged along, he might not have realized he was walking on several layers. For the ground base, medium stones were laid first. Smaller pebbles and gravel made up the next layer, topped by wide, large, smooth stones.

Concrete might be used to keep the elements in place. These roads were impressively deep--sometimes 8 feet deep. 

To keep the soldier's feet dry, the Roman road rose slightly in the middle to let water drain to the side into drainage trenches. Often arched or rectangular culverts were built underneath the road to allow water to flow underneath rather than on top of the road. Curbs along each side held in the top pavers.

Softer, unpaved paths parallel to the road were added for the unshod horses and mules.


A Roman road was  expensive to build--in some difficult terrain, perhaps $1 million per mile.

Who could travel on a Roman road?

Originally, only those on State business--the military and Rome's political leaders--could use a Roman road. The Roman State maintained a series of posts along the way so that an official could secure a fresh horse and continue onward, much like the Pony Express Rider of the American West. 

  A Roman road
A Roman Road.  Built for the military.

Groma Illustration of surveying instrument
Groma, modern illustration.

YouTube video of a person operating the groma: 


Diagram of the cross section of a Roman Road. 
Source: Pavement Interactive Wiki

In practice, a Roman road rose a bit in the middle to allow water to drain to the sides.


Aqueducts in the Roman World

To increase the size of a city or establish new ones, water was critical.

In the ancient Mediterranean world, water was always in short supply. Wells and nearby rivers simply were not sufficient.  Aqueducts were essential, and many of the 1000 cities of the Empire gained them.

The Romans were proud of their big beauties. Pliny wrote: "The terrestrial orb offers nothing more marvelous."   Remnants of the aqueducts pop up in the countryside and in cities from Rome to Spain to Turkey to North Africa.

Aspendos, Turkey. I took these photos in 2014  from the Aspendos park hillside above the aqueduct. You wander around the Aspendos site, with its forlorn smalli-ish monuments on the windy hill, until you turn a corner. The aqueduct in the distance comes marching across the valley to its counterpart.  From your vantage point on the hill, the aqueduct is slightly below, giving the sensation you can reach out and touch it.

I hadn't previously seen an aqueduct that turned a corner. At this tower, the turning angle is about 55 degrees.

Additional technical details below:

  Aspendos Turkey aqueduct
The Aspendos aqueduct marching across the valley.

Aspendos Turkey aqueduct
The  south end of the Aspendos aqueduct. The Aspendos aqueduct is famous for showing the Roman inverted siphon technique.


List of the Roman Aqueducts for City of Rome
Date Name Miles Km. Notes
312 BC Appia 10 16
272 BC Anio Vetus 40 64
144 BC Marcia 56 91 Longest
125 BC Tepula 11 18
33 BC Julia 14 22
19 BC Virgo 13 21 Flowed continuously for 2000 years
2 BC Alsentina 20 33 For Naumachia
AD 38-52 Claudia 42 69
AD 38-52 Anio Novus 53 92 Largest capacity
AD 109 Trajan 20 35 One of largest. For Baths of Trajan and Naumachia of Trajan
AD 210 Antoninina n/a   For Baths of Caracalla
AD 226 Alexandrina 14 22 For Baths of Nero
AD 537     Goths cut off aqueducts

The largest Roman aqueducts

In Rome, there were eleven major aqueducts. The largest were the Anio Novus (though its water was muddy), the Marcia, the Virgo, the Claudia, and later the Trajan.

Length of the Roman aqueducts

The longest of the eleven aqueducts for Rome, the Marcia, covered 56 miles (91.4 km). Altogether, 300 miles (480km) of aqueduct channels were built to swish water into the city of Rome.

A typical Roman aqueduct was 90%  underground. Many of the underground components have not been located. For example, only recently were the origins and the probable route of the Aqueduct of Trajan discovered:  www.aqueducthunter.com


The first of the eleven, the Appia, went up in 312 BC, in the earliest days of Rome. The last was built 500 years later, the Alexandria in AD 226.

Source of the water  

Two aqueducts originated in the northwest around Lake Bracciano, the Augusta and the mighty Trajan. Water for the others came from the south and east.

Volume of water

Ridiculous amounts of water flowed into Rome at its height. By the 5th c. AD, the 11 aqueducts in Rome fed over 1300 public fountains with drinking water, 11 imperial baths, over 900 smaller public baths, and public toilets.  Numerous private users were allowed to draw upon the aqueduct waters.

Water first flowed into reservoirs underground called "castella"  In Rome, this was big business: 247 castella have been documented.

Public toilets were a common use of aqueduct water. Your nose would have told you instantly that Ancient Rome was noticeably sweeter-smelling and more sanitary than other ancient cities.

Though the Romans did not calculate flows, we know the "carrying capacity" of ten of the aqueducts for the City of Rome was around 300 gallons of water per Roman per day. In comparison, San Francisco, CA, which today is similar in size, terrain, climate, and source of water, uses only 83 gallons per resident per day (2009).

The later Roman rulers were Las Vegas-like in their extravagant use of water in an arid climate. Emperor Augustus built a dedicated aqueduct, the Alsietina or Augusta. Its sole purpose was to flood an arena (Naumachia) for his mock sea battles.

For the Baths of Caracalla, water came from a purpose-built aqueduct--the Antonine--into cisterns that could hold over 2 million gallons.


Roman aqueducts, like Roman roads, were expensive, perhaps as much as $310,000 per mile.  In modern times, a similar water pipeline constructed in Australia has cost about 80% less.

End of the Aqueducts

The aqueducts did not collapse all at once when the Roman Empire shifted from an urban environment to a landed one. One, the Aqua Marcia,  continued to supply Rome with water well into the Middle Ages.

The Goths and other invaders did not destroy them. If invaders cut off the water supply, the Romans repaired them when the invaders moved on.

The aqueducts declined mostly from lack of demand as cities de-populated and shrunk. In the hinterlands, a lack of engineering skills among the few who remained in a city made it too difficult to maintain them. 

Elements of a Roman aqueduct system

The aqueduct business was complicated. A Roman engineer had to:

1. Find the water. Most of Rome's water came from springs in the east in the Sabine Hills, or the southeast in the Alban Hills.

2. Capture the water. The Romans used a catch basin below the spring or, if the water came from a river, a reservoir and dam.

3. Protect the water  from animals who might want to slurp it up, from evaporation into the wind, and from water-robbers. Covered channels were essential.

4. Deliver it to the city. The Romans used the flow of gravity, unaided by pumping equipment.

5. Capture the water at its destination. At the end of a Roman aqueduct, castella received and stored the water. From a castellum, water flowed to houses, fountains, baths, and workshops through a warren of pipes and underground culverts.


Gushing, rushing water--poetic but not desirable in a Roman aqueduct. Too swift and the water would overflow the channel, burst a pipe at its elbow bend, or scour out the bottom of the channel.

Too slow a flow, and the meandering trickle would pick up unhealthy sludge.

A consistent, gentle slope was the goal of the Roman engineers. The slope of the Pont du Gard aqueduct in Southern France drops only 2 feet per mile along its length of 31 miles.

Trenches:  Covered trenches followed the natural contours of the ground.

Tunnels:  Sometimes a mountain stood in the way. The Romans built a tunnel through it. Roman practice was to build tunnels from both sides of the mountain, with the two meeting in the middle. 

Sometimes they missed the mark. The excavators of the Roman Saldae aqueduct, in North Africa, misaligned their respective diggings, and the two ends did not meet in the middle of the mountain. 

Arcades and walls . Often there were shallow valleys to cross. Up went a short, solid wall with the water trench flowing on top of the wall.  In many cases, the Roman engineers built an arcade. An arcade is a bridge with a series of arches to allow people, or even a raging river, to pass underneath.

The trick was to figure out how high you could build an arched aqueduct before it collapsed. Having developed a good load-bearing arch and keystone, and using cement, the Romans could build an arch as high as 68 feet.

Stacked Arches: If a higher aqueduct were needed, the Roman engineers simply stacked another set of arches on top of the first set.

Siphon:  The begin point must be higher than the end-point. The water flowed downward. Once the initial flow reached the bottom of the valley, the water flowing from behind would force it back up the hill on the other side of the valley.

For a deep valley, the Romans might use a water-pressurized, sealed lead pipe, called an inverted siphon.

   Roman Aqueduct Claudia outside Rome today
The Roman aqueduct Claudia, outside Rome today. Courtesy: Wikipedia.

Path of aqueduct Claudia inside Rome
Path of the Roman aqueduct Claudia inside ancient Rome (reconstruction). Courtesy: VRoma

Baths of Caracalla modern artist sketch
Baths of Caracalla in Rome (artist's rendition).  Courtesy: David Darling

Built around AD 215, the Baths of Caracalla were a monument to superabundance. They could accommodate 10,000 people. Amenities included a temple, a swimming pool, cold hall, hot room, exercise courts, and perhaps a library, along with gardens and statuary.

Roman aqueducts route map
Find the water: Route map of Roman aqueducts.  
Courtesy: Evan Dembskey

 Uncovered  channel Roman Aqueduct
 Control the Flow. Uncovered specus of Pont du Gard arched aqueduct. Note relative size of the water channel.

Aspendos Turkey Acqueduct siphon and arcade
Aspendos Aqueduct,  Begin Point of the Siphon (North Tower) and Arcade.  Water for the aqueduct originated 12 miles away in the mountains. It was transported, mostly underground, to the huge north tower in the distance.  Water flowed steadily from the north tower downhill into a specus (channel  on top of the arcade. The arcade was about a mile long. Two parts are still standing.

Aspendos Turkey aqueduct
Aspendos Aqueduct End Point of the Siphon (South Tower) Once across the valley, the initial water flowed back up the hill using only gravity flow. The initial water is forced uphill by the flow of water falling downward from the North Tower, thus pushing from behind. The end-point  of the siphon, the south tower, had to be shorter than the north tower, the begin point. The Romans did not have pumps to pump water uphill, only gravity-flow and the principle of the siphon.


Roman Concrete and Arches

Two major engineering "discoveries" made the roads, aqueducts, and buildings of the Romans larger than anything else in the ancient world. Roman cement and concrete provided a way for roads and sewalls to be indestructible for 2000 years. Aqueducts could now cross raging rivers.  Roman arches made it possible for buildings, bridges, and aqueducts to bear enormous weight.

Roman concrete: in many ancient communities before the Romans, load-bearing walls had to be pretty low. Often the walls were simply rocks stacked on top of each other. The older cultures could not solve the problem of joints, the weakest point in construction. How do you bind adjacent material at the point they join together, so that the joint doesn't slip and slide and collapse when weight is added, or when  the ground shakes?  Before the Romans, the binders used to hold the joints together were weak.

The first concrete structure:  The Romans came up with something different. In the 3rd c. BC, they discovered "pozzolano," a finely ground silica from the ash of nearby volcanoes.

Combining this ash with lime and water, produced an incredibly strong, waterproof, and fire-resistant binder. Using this new binder plus aggregate, the earliest concrete structure in Rome was the platform of the Temple of Concord, built in 121 BC.

But Roman concrete--the cement plus aggregate-- by itself was not enough to keep a old-fashioned arch from falling to the ground as weight was added at the top.  A new arch design was needed.

Roman arches:  The Romans discovered (or invented) how to make that arch bear enormous weight. What they apparently realized was the importance of a the wedge-shaped stones (the "voussoir") on either side of the arch. The voussoirs had to be uniform in weight, with the keystone at the top inserted at a particular angle.

The arch and Roman expansion: The Roman-style arch was a break-through for Imperial expansion.  Roman towns no longer had to be built on rivers. Enormous aqueducts could march across the countryside and across raging rivers, carrying water from far away. Many more towns could be built, and built inland.

In buildings, Roman arches enabled temples like the Pantheon, or the Baths of Caracalla, to soar upwards unencumbered by supporting columns.

The Pantheon:  The most famous concrete structure in Rome is the Pantheon. Built in the 1st c AD and  rebuilt in the 2nd c. AD, the Pantheon is the oldest roofed building in the world. It is still intact after 1800 years.

The size of the Pantheon's dome: The Pantheon's dome is 141 feet high. It has no internal pillars to support the dome and roof. With earlier, weaker building materials, a pillar-less roof could not have been built to that height or it would have collapsed.

Roman concrete in the Pantheon: At the Pantheon, Roman cement, mixed with ever lighter aggregate as the building rose upward, enabled the roof and dome to reach its lofty height.

  Roman  Amphitheater in Pula, Croatia
Roman Amphitheater in Pula, Croatia.

In provincial Pula on the Adriatic coast (present-day Croatia,) the Romans built an amphitheater for 23,000. This for a town whose population was perhaps 30,000.

Roman arch, diagram
Engineering sketch of a Roman arch. Note the voissoirs on each side of the keystone. Sketch: Sandia National Labs.

Roman Pantheon interior
The Roman Pantheon, interior. Painting by Panini, 19th c. The National Gallery, Washington DC.)

 Roman Pantheon, side exterior, showing arches
The Pantheon's exterior arches.
From an engraving by E. Meunier, 19th c. Source: www.greatbuildings.com



Aicher, Peter, Guide to the Aqueducts of Ancient Rome. Bolchazy-Carducci, 1995

Chanson, Hubert, "The Hydraulics of Roman Aqueducts," Proceedings of the World Environmental and Water Resources Congress 2008. Ahupua'a Hawaii.

Dembskey, Evan James, The  Aqueducts of Ancient Rome. M.A. Thesis, U. of South Africa, 2009.

Evans, H, Water Distribution in Ancient Rome: The Evidence of Frontinus. U of Michigan, 1997.

Internet Resources:

Waters of Rome: GIS map and timeline Shows by decade the construction of aqueducts, water infrastructure, baths, latrines, mills, and more. Annotated. An excellent source from the University of Virginia




http://orbis.stanford.edu Orbis: the Stanford Geospatial Network Model of the Roman World

http://newscenter.lbl.gov/2014/12/15/roman-architectural-concrete/ The latest on Roman concrete by UCB scientist Marie Jackson. For advanced technical explanations, go to: https://berkeley.academia.edu/MarieJackson

Hodge, A. Trevor, Roman Aqueducts and Water Supply. Bristol, 2002.

McClellan, James E., Science and Technology in World History. Johns Hopkins UP,2006.

Oleson, John Peter, ed.,
Oxford Handbook of Engineering and Technology in the Ancient World, 2009.

Taylor, Rabun, Public Needs and Private Pleasures: Water Distribution, the Tiber river, and the Urban Development of Ancient Rome. Rome, 2000.

White, Kenneth D., Greek and Roman Technology. Cornell UP, 1984.
Updated 29 February 2016. You may contact me, Nancy Padgett, at NJPadgett@gmail.com.