Ancient Roman technology

• 1. Introduction

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  Ancient Roman technology is what held together a civilization that lasted from 753 BC to 476 AD and stretched across three continents. Some of what the Romans built was so advanced that nothing surpassed it until the 19th century. Roads, aqueducts, military siege engines, surgical tools still recognizable in modern operating rooms: the Romans produced them all. Yet many of their most sophisticated achievements were forgotten during the upheaval that followed Rome's collapse, only to be rediscovered centuries later. How did a civilization with no electricity, no steel industry, and limited sources of power manage feats that would not be matched for more than a millennium? And what exactly was lost when Rome fell?

• 2. Borrowed and Built Upon

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  Rome's engineers were, above all, talented students. Greeks, Etruscans, and Celts each contributed techniques that the Romans absorbed and extended. The Celtic peoples, for instance, supplied two pieces of technology that shaped Roman movement and logistics: the bearing, which Romans used with mud-lubricated stone rings to reduce rotational friction in wheels, and the design of the four-horned cavalry saddle. From the Minoans came the basic concept of waste disposal, a system already in existence since around 3100 BCE, when one was constructed in the Indus River Valley. Rome's genius was not always origination; it was systematization.

  Vitruvius, Pliny the Elder, and Frontinus stand among the very few ancient writers who recorded technical knowledge in detail. Most craft knowledge was transmitted privately, from a master tradesman to an apprentice, and it is theorized that tradesmen deliberately kept their methods secret. The survival of works by Archimedes, Ctesibius, and Hero of Alexandria supplemented this craftsman tradition, but not all the manuals available to Roman engineers have survived. The gaps in the record are part of why so many Roman techniques had to be painfully rediscovered by later generations.

• 3. The Power Problem

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  Moving enormous weights and running industrial machinery without fossil fuels demanded creative solutions. Human muscle, channeled through windlasses with ropes and pulleys, moved objects that exceeded what any individual could lift. On water, rowing crews powered warships in battle even though sails handled open-sea travel. Oxen, horses, mules, and donkeys each filled specific transport roles based on cost and the speed required: oxen were strong and cheap; horses were fast but expensive to feed; mules and donkeys handled passenger carriages at a middle pace.

  Water wheels provided the most scalable non-human power source. Engineers debated the tradeoffs between two designs. The undershot wheel, turned by a river's natural current pushing its submerged paddles, was far cheaper to install. The overshot wheel, fed by an aqueduct pouring water down onto its buckets from above, could be made up to 70 percent more efficient, but the cost of building the aqueduct to supply it generally outweighed the benefit. Water wheels ground grain, raised water to heights above a system's natural level, and, in at least a few documented cases, powered saws for cutting stone.

  At the mill complex at Barbegal in Roman Gaul, fed by an aqueduct, this power was concentrated on a scale that ancient historians described as the greatest known concentration of mechanical power in the ancient world. Pliny the Elder confirmed the use of similar water-powered mills at the gold mines of Dolaucothi in south Wales and at Las Medulas in north-west Spain, where at least seven major channels entered the minehead.

• 4. Stone, Cement, and Concrete

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  Pozzolana, a volcanic clay found in and around Naples, gave Roman builders a material with properties no ordinary mortar could match. Mixed at a ratio of two parts pozzolana to one part lime mortar, it could set underwater and cure to a hardness comparable to natural rock. The Pantheon's dome was built with it. When engineers constructed the Hagia Sophia, though it rose after the fall of the Western Empire, they used a pozzolana mortar substituting crushed brick dust for volcanic ash. That variant reached a tensile strength of 500 psi, compared with roughly 30 psi for a plain lime mortar, which is why the structure's mortar joints are wider than those in a typical brick-and-mortar building.

  The Pantheon's design embedded mathematical precision into its very structure. Roman engineers incorporated the concept of the perfect number, a number whose factors sum to itself, into the dome by including exactly 28 coffers. The number 28 satisfies that definition because its factors 1, 2, 4, 7, and 14 add up to 28. Scholars estimate the construction required around 400,000 man-days of labor.

  For stone quarrying, Roman workers punched holes along the desired cut line, drove wooden wedges into them, and filled the holes with water so the swelling wedges would split the block free. Blocks as large as 69 by 14 by 15 feet and weighing roughly 1,000 tons have been found. By the Imperial age, water-powered saws were cutting stone that earlier workers had shaped only by hand.

• 5. Water Across an Empire

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  Eleven aqueducts supplied the city of Rome alone, carrying more than one million cubic metres of water each day, enough to meet the needs of 3.5 million people even by modern standards, across a combined length of 350 km. Every drop moved by gravity alone, flowing through slightly slanted stone channels that drew directly from mountain springs. When those channels encountered depressions deeper than 50 metres, engineers inserted inverted siphons to push the water uphill on the far side.

  Only about 5 percent of total aqueduct water traveled across the famous arched bridges. The rest moved at ground level or underground, because bridges were more expensive to build and maintain, and spent years at a time out of service due to damage. Theft of water from the channels was frequent enough to make accurate flow measurements unreliable. To protect the channel walls from erosion, engineers lined them with a plaster called opus signinum, combining crushed terracotta with the standard pozzolana-and-lime mixture.

  The longest aqueduct traditionally attributed to Rome, running 178 km, served Carthage. The supply network for Constantinople was more complex still, drawing water from a source more than 120 km away along a sinuous route exceeding 336 km. Beyond supplying cities, aqueducts served mining operations directly. At the gold mines of Las Medulas, streams of water released onto hillsides first stripped away soil to reveal ore, then washed away rock debris in a technique known as hushing, described in detail by Pliny the Elder in book XXXIII of his Naturalis Historia and since confirmed by archaeology.

• 6. The Military Edge

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  The pilum, a javelin carried by Roman legionaries, weighed approximately five pounds. It was deliberately engineered to be destroyed on first impact so that enemies could not turn it back against Roman lines. Each soldier carried two: a primary and a backup. Polybius recorded the standard tactic of throwing the pilum and then immediately closing with swords.

  In siege warfare, the Romans adapted existing artillery, and they were probably the first to mount ballistas on carts, allowing artillery to move with a campaign rather than remain fixed. A passage from Tacitus's Histories describes an engagement in which a ballista of enormous size belonging to the Fifteenth Legion was doing great damage with the huge stones it hurled, until two soldiers disguised themselves with shields taken from the dead and cut the ropes and springs of the machine. The account conveys how decisive a single well-operated ballista could be.

  The helepolis, a siege vehicle 15 metres tall, offered a different problem in engineering: self-propulsion. Calculations suggest that at least 30 men were needed to turn a single capstan to overcome the force required to move it, or 16 men per capstan if two capstans were used, for 32 in total. An alternative gravity-powered motor used counterweights of lead or water-filled buckets, with a reciprocating water pump refilling the bucket as it descended, so motion could continue. To move a helepolis with a mass of 40 metric tons, a counterweight of 1 metric ton was sufficient.

  At sea, the corvus, a movable boarding bridge developed during the First Punic War, let Roman soldiers transfer their infantry fighting skills directly onto enemy ships. Greek fire, adopted from the Greeks in the 7th century AD and described by multiple sources as a precursor to napalm, extended Rome's naval lethality further, with its precise ingredients kept as a closely guarded military secret.

• 7. Roads, Bridges, and Medicine

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  More than 400,000 km of roads were built across the Roman world, of which 80,500 km were stone-paved. Construction began by digging a pit, often down to bedrock, filling it with rocks or gravel, topping it with concrete, and finally paving with polygonal stone slabs. The result proved so durable that after the empire's fall the roads remained usable for more than 1,000 years. A relay of horses using the dedicated courier network could move a dispatch up to 800 km in a single 24-hour period.

  Trajan's Bridge over the lower Danube, designed by Apollodorus of Damascus, held the record as the longest bridge in terms of both overall length and span length for more than a millennium. The Pons Aemilius, built in 142 BC, is the oldest surviving Roman stone bridge in Rome. Roman bridges stood at least 60 feet above the water they crossed.

  Roman medicine produced innovations that still have direct equivalents in modern surgery. Hemostatic tourniquets and arterial surgical clamps were among the tools they created or pioneered. The Roman army fielded the first known dedicated battlefield surgery unit, and Roman physicians applied a rudimentary form of antiseptic technique years before that practice gained wide acceptance in the 19th century. Dental fillings were first mentioned by Cornelius Celsus in the 1st century AD. Iron tooth implants have been found in archaeological evidence from Gaul. The drain of the Fucine Lake, at 5.6 km, was the longest tunnel Rome excavated, bored simultaneously from both ends.