Roman Engineering

Many early civilizations were known for the creativity of their people in the arts and literature, and others for the skill of their craftsmen in metal, wood and stone. The Chinese, Egyptians, and Greeks made great strides in discovering the principles of pure mathematics and science. The Chinese had reliable clocks at a very early date and Hiero of Alexandria (a Ptolemaic Greek living in Egypt) built a working steam turbine in about the year 200 BC. Certainly these early civilizations had advanced cities, which required a certain mastery of architecture and civil engineering. By comparison these ancient cities were sanitary, well defended, had an adequate water supply, and were well connected with roads to other parts of the empire or kingdom in which they were located. 

By contrast the Romans were a civilization of engineers and builders. In all of their history no great names in science or mathematics beckon to us from across the ages as those of their military geniuses or literary greats do. In the applying of pure knowledge to practical uses however, their engineers are unsurpassed until one reaches modern times. Without the ability to manufacture parts to standard dimensions close enough to allow them to be interchangeable in finished products, they nevertheless had huge factories capable of large scale mass production. Engineers traveled with their armies building roads and bridges. In fact a knowledge of engineering was almost a requirement for advancing through the ranks. After they conquered new territory and created a new province their engineers laid out cities to a standard plan and provided them with excellent roads and a clean water supply. When Julius Caesar had to cross the Rhine with his army, he built a pontoon bridge on the spot using the engineering skills of his soldiers and forced labor of the local tribesmen. Later a much larger permanent stone bridge crossed the Danube. They invented concrete using pouzzolana cement that would set and harden underwater. 
Roman roads and bridges are famous for their longevity. They were built to last a century and many have lasted 22 centuries. The Via Appia, built in 312 BC is still in use in Italy today. Roman bridges served the American General George Patton during World War II. The famous World War II general was a romantic and a history enthusiast and it gave him a sense of historical satisfaction to use bridges over which Pompey, Caesar, Sulla, Septimius Severus, and Maxentius marched their armies. Eight large aqueducts served Rome and many of those continued to provide water throughout the ages and still serve today. A Roman town was planned from the time of the original site selection for adequate water supply, sewer system, adequate production of surrounding farmland, commercial access, roads, and population density. Towns given by the emperor to retired veterans of 20 years' service (COLONIAE) were planned and built by the vets themselves. The modern German city of Cologne was just 
such a town and derives its name from its Roman designation as a COLONIA. Unfortunately, Rome itself was often poorly planned, crowded, prone to conflagration, and everything that the engineered towns weren't. 

The Romans gained much of their engineering skill from the Etruscans. From them the Romans learned the use of the keystone arch which enabled them to build extremely strong and durable bridges. The challenge in building a bridge is to create a structure strong enough to span large distances while being able to bear heavy loads and not fall down of its own weight. A small footbridge across a stream could be built of wooden logs or a flat piece of stone. When a flat piece of stone is used to bridge or span a space between two upright supports, the method is called post and lintel construction. The problem with post and lintel is that a heavy weight on the middle of the span will put too much stress on the stone and will break it if the weight is heavy enough. 
The Romans solved this problem by using a type of construction called voussoir arch with keystone. The idea behind this technical sounding term is quite simple. Imagine a ring of tapered stone blocks arranged like the diagram at the right. If one were to take a rope, wrap it around the ring, and tighten it, all it would do is force the stones more tightly together. Exchange the rope for a steel cable and tighten by twisting with a steel bar shoved between the cable and the ring and the circle of stones just becomes stronger! If a really hefty steel cable were used or the whole assembly were pounded with heavy hammers, it might fracture and pulverize, but a mighty force indeed would have to be used to destroy a ring made with this type of construction. 
To create a voussoir arch, one half of this ring of stones was simply stood up on its ends. These ends rested on piers made of stone blocks mortared together with pozzolana cement in the typical Roman arch bridge. The weight of the stone and concrete of the bridge itself compressed the tapered stones together, making the arch an extremely strong structure. Heavy wagons and legions of troops could safely cross a bridge constructed of arches without collapsing the structure. Many of these bridges lasted long after the Roman Empire in the West had fallen and survived the period of barbarian destruction of the Fifth through Ninth Centuries. Several of the original stout Roman arch bridges lasted through the midle ages and on into modern times, even serving General George Patton in the fighting during World War II just as they had served Caesar and Trajan almost two millennia before. 
Roman architects and engineers are most well known today for their roads and aqueducts. Though a shovel does not seem to be as deadly and effective a weapon in the hands of a Roman soldier as his famous gladius, it was soldiers with shovels that built most of the roads that tied the mighty Roman Empire together for five hundred years. Because of the priority the Roman government placed on building wide, durable, all weather roads, an army could be sent to a trouble spot in the farthest corner of the Empire and arrive there within six weeks. 
Roman engineers designed their roads to provide a solid surface on which to drive chariots and freight wagons or to move thousands of soldiers quickly. They had to be well drained so that rainwater did not build up and weaken them and they often had to cross wide stretches of wet or marshy ground without collapsing under the weight of an army legion and its heavy supply wagons. Roman roads were constructed with a foundation of rock so that they would not sink out of sight when the ground was waterlogged and would not wash away with the runoff from the spring thaw and rains. 
To build a road, a work crew often consisting of soldiers or slaves under the supervision of soldiers would first dig two ditches. 
Most modern people think of concrete as a modern invention. In fact Cities of glass and concrete is a saying that is often used to describe our modern cities. The cliche is often used as a metaphor for the fast paced, mass produced, somewhat artificial nature of the modern life we lead. It would surprise most people to learn that the ancient Egyptians used concrete in the construction of buildings, and the Romans had refined the art of concrete making down to a precise technology. They didn't understand that concrete gained its strength by actually incorporating water into the molecules of artificial limestone as modern chemistry has told us, but they did know that water actually makes the concrete stronger. 

The formula for making concrete has been known since the time of ancient Egypt and Mesopotamia. Limestone was roasted until all of the water locked within its molecules was driven off and it became powdered lime. The lime was mixed with sand to make mortar for bricls, and with sand and gravel to make the familiar gray concrete that is as much a part of our cities today as it was in the days of the Romans. 
The Romans did discover one extra ingredient to add to their concrete that gave it the durability to last through twenty centuries of rain, wind, freezing temperatures, and even the scouring action of sand in a fast moving river current. Pozzolana, a fine grained volcanic sand, was very hard and could resist wear and abrasion better than the soft lime which bound the pieces of gravel together in regular concete made only of lime, sand, and gravel. The Romans soon learned to make their bridge piers from pozzolana concrete to keep the sand borne by river currents from eroding away the foundations of their bridges below the water. Today, modern industrial chemists use silica from blast furnace slag to replace the pozzolana used by the Romans when making portland cement used in construction but many bridges and other structures made with pozzolana concrete by the Romans are still in daily use. 

Most cities in the ancient world tended to grow up around a place that was near water, on an existing trade route and was easy to defend against attack. As the ancient empires in Mesopotamia, China, and Egypt grew larger to conquer and govern more territory, their more important cities had to grow as well. Most cities started out small and just grew, with little thought given to planning their growth by the emperor or ruler governing them until after they had become a large, thriving metropolis. By this time, they may have outgrown their original walls two or three times. Their older sections had narrow, crooked streets with houses and shops that were too small and too close together. This invited the spread of fire and disease, problems that all overcrowded cities face. In fact, Rome was almost completely destroyed by fire several times during the First Century AD The infamous fire of AD 64 which Nero tried to blame on the Christians was actually a regular occurrence. Fire swept through the overcrowded poorer districts of Rome every eight to ten years. 

It was in the planning of new towns that the genius of Roman enginers and civic planners was given a chance to create a city of lasting beauty and orderly efficiency. When small to medium sized cities were built where there had been only empty land, Roman engineers often followed a standard plan based on the Roman army camp or castra. These thorough people with their measuring rods and gromas that would meet the needs of its growing population for many years to come. 

The Romans' skill in civil engineering is one of the things that contributed greatly to the establishment of their civilization and empire. Their roads and bridges tied their empire together and made travel easier for Roman merchants, soldiers, and citizens (and pirates, for that matter). Their temples and great public buildings beautified their cities and many still stand as a testimony to their greatness. But it is the Romans' system of supplying water to their cities that, in this author's opinion, distinguishes the Romans as an advanced, modern civilization emerging from classical antiquity. 
When human beings come to live together in communities any larger than small villages, the supply of water and the removal of waste become critical issues. The way these issues are dealt with determines whether the growing village becomes a thriving city or a backward and disease - ridden community. In small communities, individual households could manage the job of supplying themselves with fresh water from a stream or well. Likewise, it was the individual's responsibility to remove waste and garbage by burying it or carrying it beyond the walls of the village. As the village grew into a town, these jobs grew too large for the individuals to deal with efficiently and civic government had to take over. The Romans solved these problems by calling on their civil engineers to plan and build a centralized water distribution network and sewage system for every major town or city in the Republic. By the time of the late Republic and early Empire, Rome could boast one million inhabitants and several cities were home to several hundred thousand souls. The water supply to Roman cities had to reliably provide a continuous supply of fresh, clean water in order for these cities to survive. Likewise, an efficient sewer system had to be able to carry away wastewater from homes and buildings, as well as provide drainage for low areas of the city that might become swampy areas after a rainstorm. 

Essentially the way the Romans were able to supply water to their cities and cause the fountains in their cities to flow continuously was to use a system of aqueducts with a constant gradient and a system of cisterns and manifolds to hold and distribute the water. In non - engineering terms, a gradient is simply a slope expressed in numbers. The aqueducts and tunnels through hills that have survived have gradients ranging from one foot drop per 150 feet of length to one foot drop in about 500 feet of length. The Roman engineer Vitruvius recommended a gradient of not less than 1 in 200. By carefully choosing the gradient and maintaining it along the entire length of the aqueduct, the water could be made to flow fast enough to ensure a good supply yet not so fast that the aqueducts and pipes were washed out by the force of rushing water. The aqueducts usually went through tunnels when a hill lay in the way between a town and a water source. When the aqueducts crossed valleys or low places, they were built on top of arched causeways. Sometimes, when a very high aqueduct was needed, there were three courses of arches, one on top of the other, with the arches becoming smaller toward the top. A very beautiful example of this is the Pont du Gard near Nimes, in France, built while France was still the Roman province of Gaul. Some ancient cities just grew up on likely or easily defended spots, while some were very carefully planned out and engineered before a single street or building was built. In the latter case, the engineers would prospect for natural water sources and have a good idea of how much water they would supply before deciding on how large to make the town. Of course, the problem of urban sprawl and overpopulation often caused the city to outgrow its water supply if too many people moved in after the planning and engineering had been done, but the engineers would try to plan for this as well as they could. The type of water source they liked best was an artesian well or natural spring at the foot of a hill where the water flowed out all on its own. After carefully planning the gradient and building the aqueduct, they could expect a certain rate of flow of water from the source to the town. A well engineered system even took into account that there might be less water available from a spring during the Summer months. A good artesian well, however, would supply water at a constant rate all year long if one did not try to take more water out than it could supply. 

After the water had flowed down the aqueduct into the town, it was usually directed into a manifold, or large distribution tank which feeds several large water mains that lead off into different areas of the city. This structure was constructed of masonry walls and was situated far enough above street level to cause water to flow at a reasonable rate by gravity into the city or town's water mains. These water mains were pipes made of sheet lead or terra cotta. The lead pipes were usually round or triangular in cross section and formed from a rectangular sheet of lead. The lead was rolled into a tube or folded into a triangle shape and the edges soldered together or folded over, crimped, and soldered together. The fountains were located on many street corners and water flowed into them by gravity. The excess water would flow down into another set of pipes to feed other fountains at lower levels throughout the hilly city of Rome. Finally, water would flow from the last in a chain of fountains into the cloaca, or city sewer system which would then discharge into a river as sewage. It was not the Romans' practice to turn the fountains off even though they knew how to build a valve to control the water. 

In the city of Rome, the aqueducts and the fountains they fed have been in use for centuries. Many of the ones in use today were built by the Romans between 312 BC and 200 AD. The first of Rome's eleven ancient aqueducts was built by the censor Appius Claudius Caecus in 312 BC. This is the same Appius Claudius Caecus who built the Via Appia, a road leading south out of Rome toward the territory of the Samnites, with whom the Romans were at war at that time. He is less well remembered in the popular mind as the builder of the Aqua Appia, the first aqueduct to carry water to the fast growing city of Rome. During ancient times, the city of Rome had between 1200 and 1300 public fountains, eleven large scale public baths, 867 smaller baths, and two artificial lakes used for mock naval battles. The city's eleven aqueducts delivered 38 million gallons of water to the city every day. 
Managing such a large and complex municipal public works project as the water supply for the city of Rome required quite a lot of manpower. During the late First Century AD, Sextus Julius Frontinus, the curator aquarum or city official in charge of the water supply had seven hundred trained slaves in addition to several civil engineers who specialized in water and aqueducts working for him. 
It is interesting to note that water was delivered to private homes via the city's water mains and metered with officially calibrated nozzles which were given an official stamp. Water usage into private homes was taxed, and two classes of service were available. Small houses were allowed a one half inch pipe connection to the water mains, while larger houses with baths were allowed a one and one half inch connection. When Frontinus first came into office, he audited the books and found that much more water was being used than could be accounted for in official records. He ordered his slaves to investigate, and found many illegal connections to the city's water system. He even found corruption in his own department, as many users had bribed his workers to allow them to tap into the water mains illegally so they could irrigate their gardens and crops. Frontinus prepared a very detailed record of the design and construction of Rome's water supply titled De Aquis Urbis Romae. 

During the Fifth Century AD, most of the city's aqueducts were destroyed by the Ostrogothic warlord Vitiges when he placed Rome under siege during the war with the Byzantine emperor Justinian. Vitiges was not able to cut the city off entirely from its water supply, though, as he missed the Aqua Virgo. Most of this aqueduct runs underground. 
During the Fifteenth Century, the popes began restoring Rome's aqueducts, most of which had fallen into disrepair after more than one thousand years. In 1429, while doing research at the library of Monte Cassino, a secretary to Pope Nicholas V happened upon De Aquis Urbis Romae, Frontinus' long forgotten manuscript describing the water works of Rome. Using this manuscript, workers were able to locate and repair the Aqua Virgo. From the Renaissance up until the time when Italy became a modern nation in the Nineteenth Century, the restoration of Rome's aqueducts was undertaken and financed by several of the popes. 

House walls were plastered and painted with decorative panels, scenes from mythology or from daily life. Exteriors, and walls of the less wealthy, might be bright solid colors (often an ocher yellow) or marked and painted to resemble stone. Columns of stone, wood, or intricately shaped bricks, plastered and painted to look like stone, supported the roof. The roof beams were generally of wood, though stone might be used as well for short spans. Both Etruscans and Romans used the arch and the vault, though the possibilities opened up by arch construction were not fully explored until later. Wealthy homes might also boast of an interior garden, the peristyle garden, centered by a fountain and surrounded by a colonnade, columns supporting the roof of a covered walkway. Lead gutters and pipes channeled rainwater from the roof into storage for the household. 
Terra cotta, the familiar baked red clay of modern flower pots, was used extensively by the Etruscans for roof tiles, column capitals, decorative friezes around the tops of buildings, statues, pots and other household uses. The Romans preferred stone or marble for most structural and decorative uses, copying the Greeks, but must have appreciated the way terra cotta remains impervious to weather (unlike the soft volcanic stone of the area around Rome) and continue to use it for roof tiles to this day. Roman roofs were made of overlapping tiles: "tegulae," flat, basically rectangular ones with flanges along the sides, and "imbrices," half-tubes to cap the space over the flanges. Fittings for the corners and edges of the roof, to direct rainwater and for decoration, were also of terra cotta, often molded as fantastic or grotesque faces. 
Doors and window shutters from Republican Rome were generally of wood, though they might be reinforced with iron. Ironwork gates and grills provided security. Evidence of paneled and louvered designs similar to what we use today have been discovered in Pompeii. A noticeable difference was in placement. The Roman domus opened inward. The front entrance was often the only entrance to the house, although there might be an additional service gate to a back alley. Wide doorways with draperies and folding doors of louvered panels opened the dining rooms and other public areas to the atrium or peristyle garden. No windows opened onto the street at all. 
The closest thing to a modern window in urban houses was an occasional opening, often covered by a grillwork of wood or iron, probably just to let in light. Windows might also be covered with translucent materials such as oiled sheepskin or thin sheets of mica or gypsum. By the time of Augustus, the Phoenicians had learned to blow glass, and to create sheets of it clear enough for windows. The Romans, true to their common practice of adopting anything from other cultures that made for a better quality of life, soon were adding glazed windows to their houses. 

The urban domus might include shops opening onto the street. Ruins show channels in the door frames and sills of these shops that apparently held the ends of a door that may have pulled down something like the cover of a roll top desk or a modern garage door. These were surely made of wooden boards, but historians don't know how they were held together with canvas, leather, or iron rings, perhaps. 
Multi story apartment houses, insula or islands were home to urban Romans who couldn't afford their own domus. The ground floor was generally set aside for shops or other commercial use. The next floors might have two or four luxury apartments, with the density increasing and the apartment size decreasing on upper floors. Before the days of elevators, there was no such thing as a penthouse. Augustus limited the height of insulae in Rome to 70 ft and a later emperor to 60, so seven or eight stories may have been relatively common. Writers of the Republican period complained of the dangers to inhabitants of the insulae, that they often burned or collapsed, killing those who lived there. The remains discovered seem to be of sturdy, well-constructed buildings, but that may be because the worst ones had all been replaced in ancient times. 
These ancient apartment houses in addition to the obvious differences, like no electricity and no bathrooms on upper floors, we might notice the lack of hallways. A great deal of space was used up by multiple stairways serving only apartments directly above one another. The rooms within an apartment opened directly into each other, so that if there were multiple bedrooms one might have to walk through one to get to another. 

The walls of buildings in the ancient Mediterranean world were generally brick or masonry rather than wood. They were thick by modern standards, often one and a half to two feet in buildings of only two stories, and thicker in proportion for taller buildings. 
The Greeks built their walls of stone blocks cut and trimmed into equal rectangles. The wall looked much like a modern brick wall built with the joints between the bricks alternating in each layer. Greek walls were two blocks wide, with occasional blocks or courses laid crosswise to bind the two rows together. Romans sometimes built in this Greek fashion called opus quadratum. 
For buildings of heroic size the Romans sometimes built with huge blocks of volcanic tufa. Tufa is relatively porous and lightweight for stone, but the blocks still weighed many tons. Early builders may have used ramps of sand or earth, as is speculated for the Egyptians. But Vitruvius describes several machines for lifting and placing stones of great weight, ropes and pulleys supported by cranes and frames of poles. Rather than use lime mortar, which dried out and cracked when used with porous stone, the Romans precisely cut and fit the stones together and held them together with clamps of bronze or iron. Today we see these walls as massive pockmarked ruins, their clothing of marble and metal clamps pillaged by the builders of the Renaissance, who used the ancient buildings of Rome as their quarry. 

Instead of a solid wall of bricks or stone blocks, a Roman wall more often had facings of brick or stone, a cavity in the center filled with rubble and mortar or packed clay, and a coating of plaster. Roman bricks were large and flat by modern standards, approximately eight by eighteen by one and one-half inches. Common brick was mud-brick, and even if it was cured the recommended two years before being used, it was sensitive to moisture and weathering. This, and the fact that the stone available around Rome was a relatively soft material, volcanic tufa or limestone, surely led to the practice of plastering walls inside and out. Fired, or "burnt" brick was also used for construction, as was recycled terra cotta roof tile. Vitruvius reports that only burnt brick could be used for new construction of insulae in Rome during his time, as common brick, or mud brick, walls needed to be thicker than regulations allowed. Perhaps that is why the ruins of the relatively newer insulae at Ostia survived into modern times. 
Stone walls or facings might also be made of trimmed rectangular stones of irregular sizes, opus incertum. The stones could not be laid in straight courses, but when carefully fitted together with some stones extending deep into the wall or even through to the other side, this pattern made for a very strong wall. These patterns of construction depended on lime mortar to hold the elements together. 

Ruins often reveal that stone or brick was precisely laid at a building's front, corners and around doorways, and less regularly at the back and the walls between. Vitruvius reports that basketwork, lath or cane woven together and covered with mortar or plaster, might be used by the poor or for interior walls particularly on upper stories. This construction was neither moisture resistant nor fireproof but it was lightweight, cheap and quickly built. Of course these walls have not survived. 
About the third century BC, Roman builders discovered that volcanic ash when added to lime mortar made a cement that cured to a rocklike hardness even under water. Mixed with sand and gravel this material was the equivalent of modern concrete. At first concrete was used like a particularly durable mortar, or for places where its ability to harden without drying out was important for the water courses of aquaducts and for bridge pilings, for example. 
In the time of the Republic the core of a wall would be concrete, but the facings remained brick or stone. At first, the concrete might be poured between facings of masonry, and layers of rubble added. 
Eventually, walls became essentially a mass of concrete, poured into a wooden form and finished before it was completely set. The old terms acquired new meanings. Opus testaceum referred to a concrete wall in which wedge shaped pieces of brick were inserted, point first, so that the wall appeared to be of laid brick. Opus incertum referred to a concrete wall in which irregular chunks of stone were pressed into the soft concrete. When the concrete set, the stones were chiseled down even with the concrete surface. Opus reticulatum or netlike work in which little square pyramids of stone were inserted point first in a diamond pattern became quite popular. This pattern appears as the flat surfaces of walls between corners of laid brick or stone. According to Vitruvius, opus incertum is an ancient style, and opus reticulatum, while not as strong is the style used by everybody. 

By the year 1000 BC the technology for making bronze, brass, and other copper alloys was quite well understood by all civilizations and even most primitive societies in Europe, Asia, and North Africa. The temperatures of 1300 to 1400 degrees Fahrenheit were by then easily attained in copper smelters and pottery kilns. With iron it was a totally different story. Iron requires temperatures of about 3000 degrees Fahrenheit to properly separate it from its ores and obtain metal in liquid form that can be cast into molds. It was only in the Middle Ages that Europeans learned to achieve these kinds of temperatures in their iron smelting furnaces. If the high temperatures required weren't enough of a challenge, the handling of iron once it has been heated to high temperatures is quite tricky. It wants to combine with any available oxygen in the fiercest way and will burn brightly at temperatures lower than those required to melt it. Early metalsmiths discovered that an impure form of spongy iron could be extracted from its ore if the ore were heated in the presence of plenty of charcoal with air forced through the burning mixture in a sealed furnace. The charcoal burned very hotly and at the same time kept all available oxygen away from the iron by using it to keep up its own fire. 

The fineness or proportion of precious metal in an alloy was most important in commerce and archaeological research has shown that the Romans could control the finess of gold in their coins and ingots to within one percent. This degree of control not only allowed the Romans to closely guard the purity of their gold and silver coins but allowed them to cheat accurately as well. 
An alloy of copper and zinc called orichalcum was used a great deal by the Romans. This consisted of eighty percent copper and twenty percent zinc, with small amounts of lead, tin, and other metals and would be called yellow brass today. 

When Rome was still a tiny village on the Palatine Hill. Phoenician traders were sailing their ships the length and breadth of the Mediterranean and beyond in search of goods to be sold or traded for a handsome profit. There were great risks in making a long sea voyage and bringing home a valuable cargo, but the enormous profit that could be made from selling the goods made the risks worthwhile. The key was to trade a product that was unique, very desirable, hard to get, or desperately needed for other products that were common in the land of the people with whom you were trading. These products may be rare and desirable someplace else, and the trader now had something with which he could once again make a profit. 
Tin was just such a product in the ancient world. Our technology today would not be possible without oil and electricity. In the same way, tin was vital to the ancients because it was needed in the making of bronze. Bronze was an alloy, or a mixture of two or more metals. To make bronze, the metalsmith mixed copper with the proper amount of tin. Copper tools and weapons by themselves were too soft and did not long remain sharp. Tin made the copper harder and also made the molten metal fill the mold more completely when it was cast into useful objects like axe heads, hammers and jewelry. So many useful articles were made of bronze in ancient times that no civilization could thrive very long without a supply of it or the copper and tin needed to make it. The secrets of making iron were well known by the time the Romans made their entrance into history but iron products were difficult to make and rusted easily. Besides it was hard to make iron that didn't have cracks and weak spots. With hard work and a skilled craftsman, good iron tools and weapons could be had but bronze was much more suitable for most metal articles. 

The deposits of tin in the ancient world were usually small and not very plentiful. The Phoenicians discovered the tin deposits of the British Isles either from an early explorer or through their own exploring and seeking out of new products and markets for them. They kept the knowledge of the Cornish tin mines a closely guarded secret so they could control trade in the metal and charge a high price for it. After the Punic wars, Carthage, the one remaining city of the Phoenicians, became less and less an important economic power. With their well - known efficiency and thoroughness, the Romans counted access to the British tin mines as one of the advantages of conquering the island. Julius Caesar knew of the importance of British tin when he invaded the island in 55 to 54 BC After the conquest of Britain during the reign of Claudius, the Romans were in control of most of the world's supply of the metal. The province of Britain was not a highly profitable one to the Romans, but tin was one commodity that made it essential for the Romans to conquer and keep this remote part of their vast empire. 

The Roman Era