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5 Engineering Feats from the Roman Empire

5 Engineering Feats from the Roman Empire

Roman engineers designed and built stone and concrete bridges and other infrastructure using early cranes and a concrete mix that has held up for two thousand years.
The Roman Empire was one of the greatest civilizations in history. Its reach of influence was due in large part to its large-scale engineering accomplishments. Critical to these developments is the concrete used by Roman engineers. Many examples can still be found in surviving infrastructure such as far-reaching, long-lasting road systems, along which the military could move its invading armies as well as facilitate trade and cultural exchange.

Here are five of ancient Rome’s greatest engineering feats—some of which are still operational today.

1. Aqueducts

Roman engineers built complex systems of aqueducts to bring fresh water into their growing cities and towns from the surrounding countryside. Relying on gravity only, water flowed from these complex networks of underground pipes, above-ground water lines, and bridges into large holding areas. The water was then distributed to public baths, fountains, and private homes. Some of these aqueduct elements still supply water to fountains in the city of Rome.

2. Roads

Roman roads consisted of dirt and gravel with bricks quarried from hard volcanic lava or granite, making the roads strong and durable. The first phase of construction involved digging a three-foot-deep trench that served as the base of the planned road. Bricks were set in the bottom of the trench and covered with gravel to facilitate drainage. The final step was adding a top layer of flagstones, which tilted slightly to the sides to allow water to run off. By 200 A.D. the Romans had built more than 50,000 roads.

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3. Bridges

The arch structure allowed for longer spans and made Roman bridges incredibly strong. Roman engineers favored semicircular arch bridges but also utilized segmental arch bridges. For making concrete piers in riverbeds, they developed the cofferdam, which diverted water so they could shape and set the piers. One of the best examples of Roman bridge-building is the bridge over the Tagus River in Alcantara, Spain. Its arch stones weighed up to eight tons each and were so perfectly shaped that no mortar was needed in the joints. The bridge still stands today, 2,000 years later.

4. Sewers

The vast Roman sewer system began simply as a trench to drain some nearby wetlands. Surrounding communities began building their own trenches to connect to this the main trench. Building materials consisted of masonry, concrete, and sometimes lead piping. This growing sanitation system was flushed regularly, with the wastewater running off into streams and marshland. The city covered the gutter systems and added public bathrooms, which helped keep the streets clear of human waste and reduce unpleasant smells. This greatly improved public health; however, the downside was that the Tiber River became absolutely swollen with human waste. Parts of this vast sewer system still function today.

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5. Heated floors

The Romans invented what we know today as radiant floor heating. “Hypocausts” consisted of hollow clay columns spaced every few feet below a floor that was supported by concrete pillars. Hot air and steam were circulated through these columns from an underground fire in a nearby room into the occupied space above. Flues were also built into the walls to ensure the heat could rise to the higher floors, where the fumes were eventually vented through the roof.

Ancient Rome’s magnificent feats of engineering would not have been possible without opus caementicium—Roman concrete. This unique mix of sand, lime, and volcanic ash is so strong and durable that it has barely started to decompose over 2,000 years. Several types of Roman concrete could even be set underwater. Perhaps the most impressive concrete structure from ancient Rome is the Pantheon, which still stands as the largest unreinforced concrete structure in the world.

Modern researchers have studied Roman concrete for decades in attempts to duplicate its chemical secrets. Scientists discovered that volcanic ash plays a critical role in both hot and non-hot mixing. Massachusetts Institute of Technology researchers have recently discovered that lime clasts incorporated into the concrete are a key self-healing component: When lime clasts get wet, they release calcium that fill pores and cracks in the concrete over time, strengthening it from within. Engineers are hopeful this knowledge can be used to develop more durable concretes, especially for corrosive environments.

Mark Crawford is a science and technology writer in Corrales, N.M.

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