Roman trade was the engine that drove the Roman economy of the late Republic and the early Empire. Fashions and trends in historiography and in popular culture have tended to neglect the economic basis of the empire in favor of the lingua franca of Latin and the exploits of the Roman legions. The language and the legions were supported by trade while being at the same time part of its backbone. Romans were businessmen and the longevity of their empire was due to their commercial trade.
Whereas in theory members of the Roman Senate and their sons were restricted when engaging in trade, the members of the Equestrian order were involved in businesses, despite their upper class values that laid the emphasis on military pursuits and leisure activities. Plebeians and freedmen held shop or manned stalls at markets while vast quantities of slaves did most of the hard work. The slaves were themselves also the subject of commercial transactions. Their high proportion in society (compared to that in Classical Greece), and the reality of runaways, the Roman Servile Wars and minor uprisings, they gave a distinct flavor to Roman commerce.
The intricate, complex, and extensive accounting of Roman trade was conducted with counting boards and the Roman abacus. The abacus, using Roman numerals, was ideally suited to the counting of Roman currency and tallying of Roman measures.
Negotiatores, mercatores and pedlars 
The Romans knew two types of businessmen, the negotiatores and the mercatores. The negotiatores were in part bankers because they lent money on interest. They also bought and sold staples in bulk or did commerce in wholesale quantities of goods. In some instances the argentarii are considered as a subset of the negotiatores and in others as a group apart. The argentarii acted as agents in public or private auctions, kept deposits of money for individuals, cashed cheques (prescriptio) and served as moneychangers. They kept strict books, or tabulae, which were considered as legal proof by the courts. The argentarii sometimes did the same kind of work as the mensarii, who were public bankers appointed by the state. The mercatores were usually plebeians or freedmen. They were present in all the open-air markets or covered shops, manning stalls or hawking goods by the side of the road. They were also present near Roman military camps during campaigns, where they sold food and clothing to the soldiers and paid cash for any booty coming from military activities.
There is some information on the economy of Roman Palestine from Jewish sources of around the 3rd century AD. Itinerant pedlars (rochel) took spices and perfumes to the rural population. This suggests that the economic benefits of the Empire did reach, at least, the upper levels of the peasantry.
Commercial infrastructure 
The Forum Cuppedinis in ancient Rome was a market which offered general goods. At least four other large markets specialized in specific goods such as cattle, wine, fish and herbs and vegetables, but the Roman forum drew the bulk of the traffic. All new cities, like Timgad, were laid out according to an orthogonal grid plan which facilitated transportation and commerce. The cities were connected by good roads. Navigable rivers were extensively used and some canals were dug but neither leave such clear archaeology as roads and consequently they tend to be underestimated. A major mechanism for the expansion of trade was peace. All settlements, especially the smaller ones, could be located in economically rational positions. Before and after the Roman Empire, hilltop defensive positions were preferred for small settlements and piracy made coastal settlement particularly hazardous for all but the largest cities.
By the 1st century, the provinces of the Roman Empire were trading huge volumes of commodities to one another by sea routes. There was an increasing tendency for specialization, particularly in manufacturing, agriculture and mining. Some provinces specialized in producing certain types of goods, such as grain in Egypt and North Africa and wine and olive oil in Italy, Hispania and Greece.
Knowledge of the Roman economy is extremely patchy. The vast bulk of traded goods, being agricultural, normally leave no direct archaeology. Very exceptionally, as at Berenice, there is evidence of long distance trade in pepper, almonds, hazelnuts, stone pine cones, walnuts, coconuts, apricots and peaches besides the more expected figs, raisins and dates (Cappers). The wine, olive oil and garum (fermented fish sauce) trades were exceptional in leaving amphorae behind. There is a single reference of the Syrian export of kipi stiff quince jam or marmalade to Rome.
Land routes 
Even before the republic, the Roman Kingdom was engaged in regular commerce using the river Tiber. Before the Punic Wars completely changed the nature of commerce in the Mediterranean, the Roman republic had important commercial exchanges with Carthage. It entered into several commercial and political agreements with its rival city in addition to engaging in simple retail trading. The Roman Empire traded with the Chinese (via Parthian and other intermediaries) over the Silk Road (see Romano-Chinese relations).
Sea routes 
Maritime archeology and ancient manuscripts from classical antiquity show evidence of vast Roman commercial fleets. The most substantial remains from this commerce are the infrastructure remains of harbors, moles, warehouses and lighthouses at ports such as Civitavecchia, Ostia, Portus, Leptis Magna and Caesarea Maritima. At Rome itself, Monte Testaccio is a tribute to the scale of this commerce. As with most Roman technology, the Roman seagoing commercial ships had no significant advances over Greek ships of the previous centuries, though the lead sheeting of hulls for protection seems to have been more common. The Romans used round hulled sailing ships. Continuous Mediterranean "police" protection over several centuries was one of the main factors of success of Roman commerce, given that Roman roads were designed more for feet or hooves than for wheels, and could not support the economical transport of goods over long distances. The Roman ships used would have been easy prey for pirates had it not been for the fleets of Liburnian galleys and triremes of the Roman navy.
Bulky low-valued commodities, like grain and construction materials were traded only by sea routes, since the cost of sea transportation was 60 times lower than land. Staple goods and commodities like cereals for making bread and papyrus scrolls for book production were imported from Ptolemaic Egypt to Italy in a continuous fashion.
The trade over the Indian Ocean blossomed in the 1st and 2nd century AD. The sailors made use of the monsoon to cross the ocean from the ports of Berenice, Leulos Limen and Myos Hormos on the Red Sea coast of Roman Egypt to the ports of Muziris and Nelkynda in Malabar coast. The main trading partners in southern India were the Tamil dynasties of the Pandyas, Cholas and Cheras. Many Roman artifacts have been found in India; for example, at the archaeological site of Arikamedu, in Puducherry. Meticulous descriptions of the ports and items of trade around the Indian Ocean can be found in the Greek work Periplus of the Erythraean Sea (see article on Indo-Roman trade).
Standard weights and measures 
A standard amphora, the amphora capitolina, was kept in the temple of Jupiter on the Capitoline Hill in Rome, so that others could be compared to it. The Roman system of measurement was built on the Greek system with Egyptian influences. Much of it was based on weight. The Roman units were accurate and well documented. Distances were measured, and systematically inscribed on stone by agents of the government.
A fairly standard and fairly stable and abundant currency, at least up to c. 200 AD, did much to facilitate trade. (Egypt had its own currency in this period and some provincial cities also issued their own coins.)
Contacts with India and China 
The trade over the Indian Ocean blossomed in the 1st and 2nd century AD. The sailors made use of the monsoon to cross the ocean from the ports of Berenice, Leulos Limen and Myos Hormos on the Red Sea coast of Roman Egypt to the ports of Muziris and Nelkynda in Malabar coast  and. The main trading partners in southern India were the Tamil dynasties of the Pandyas, Cholas and Cheras. Meticulous descriptions of the ports and items of trade around the Indian Ocean can be found in the Periplus of the Erythraean Sea. The main articles of trade with India were spices such as pepper, cardamom, cloves, cinnamon, sandal wood and gems such as pearls, rubies, diamonds, emeralds and ivory. In exchange the Romans traded silver and gold with India.
Pomponius Mela (Book III,Chapter 5), copied by Pliny the Elder, wrote that Quintus Caecilius Metellus Celer, proconsul in Gaul, 59 BC, got 'several Indians' (Indi) as a present from a Germanic king. The Indians were driven by a storm to the coasts of Germania (in tempestatem ex Indicis aequoribus):
- Metellus Celer recalls the following: when he was Proconsul in Gaul, he was given people from India by the king of the Sueves; upon asking why they were in this land, he learnt that they were caught in a storm away from India, that they became castaways, and finally landed on the coasts of Germany. They thus resisted the sea, but suffered from the cold for the rest of their travel, and that is the reason why they left. (Sueves is an emendation to the text.)
It is unclear whether these castaways were people from India or Eastern Asia, since "Indians" designated all Asians, Indian and beyond, during Roman times. Pomponius is using these Indi as evidence for the Northeast Passage and the northward strait out of the Caspian Sea (which in Antiquity was usually thought to be open to Oceanus in the north). Edward Herbert Bunbury suggests that they were of Finnish origin. There are also some speculations that they may have been American Indians castaway across the Atlantic.
Some confusion may be suspected in this passage since Metellus Celer died before taking up his proconsulship, thus leaving it free for Julius Caesar.
Hoards of Roman coins have been found in southern India during the history of Roman-India trade. Roman objects have been found in India in the seaside port city of Arikamedu, which was a center of trade during this era.
The Hou Hanshu (History of the Later Han Chinese dynasty) recounted the first of several Roman embassies to China sent out by a Roman Emperor, probably Marcus Aurelius judging by the arrival date of 166 (Antoninus Pius is another possibility, but he died in 161. The confusion arises because Marcus Aurelius took the names of his predecessor as additional names, as a mark of respect and so is referred to in Chinese history as "An Tun", i.e. "Antoninus"). The mission came from the South, and therefore probably by sea, entering China by the frontier of Jinan or Tonkin. It brought presents of rhinoceros horns, ivory, and tortoise shell which had probably been acquired in Southern Asia.
The mission reached the Chinese capital of Luoyang in 166 and was met by Emperor Huan of the Han Dynasty. About the same time, and possibly through this embassy, the Chinese acquired a treatise of astronomy from Daqin (Rome).
However, in the absence of any record of this on the Roman side of the silk road, it may be that the "ambassadors" were in reality free traders acting independently of Aurelius.
From the 3rd century a Chinese text, the Weilue, describes the products of the Roman Empire and the routes to it.
Commerce and religion 
Mercury, who was originally only the god of the mercatores and the grain trade eventually became the god of all who were involved in commercial activities. On the Mercuralia on May 14, a Roman merchant would do the proper rituals of devotion to Mercury and beseech the god to remove from him and from his belongings the guilt coming from all the cheating he had done to his customers and suppliers.
The Elite and a duel mentality on trade 
While Livy makes reference to the Lex Claudia (218BCE) restricting senators and sons of senators from owning a ship with greater than 300 amphorae capacity (about seven tons), they were still undoubtedly partaking in trade as Cicero mentions this law when attacking Verres, although he makes no move to charge him.
Senators were still allowed to own and make use of ships under the size restriction, Cato when advising where to build a farm specifically mentions to have it built near an accessible river, road or port to allow transport of goods which is in direct conflict to Livy’s assertion that all profit made through trade by a senator was dishonorable.
That is not to say that the acquisition of wealth was not to be desired, Pliny notes that a Roman man should by honorable means acquire a large fortune and Polybius draws a comparison between the attitudes of Carthage and Rome towards profit from trade. Thus starts the confusion in the role of the elite in trade as Terrence writes that there is nothing wrong with large scale trade, it is in fact completely honorable and legitimate to import large quantities of product from around the world especially if it happens to lead to a successful trader buying land and investing in roman agriculture; what is dishonorable is trade on a small scale. Small trade is again shown as vulgar by Tacitus as he describes the involvement of Sempronius Gracchus in petty trade.
Cato himself was involved with trade, although he himself cautioned against it as it was a risky occupation, perhaps this was part of the reasoning to keep senators excluded from the trade business, as if they had a severe misfortune with trading they could fall below the financial threshold of being a senator, were as comparatively land owning was a far safer investment. Plutarch describes Cato’s involvement in trade in great detail, depicting how he would use a proxy (a freedman by the name of Quintio) to run his business through a group of fifty other men.
The restriction on senators trading was itself passed initially through the tribune of the plebs, a class of people who the restrictions would not apply to. It is suspected that this reform could have been the equites and other wealthy merchants trying to muscle the senators out from the rapidly expanding trade business.
Commercial Classes 
The majority of the people of the Roman Empire were living in destitution, with an insignificant part of the population engaged in commerce, being much poorer than the elite. The industrial output was minimal, due to the fact that the majority poor could not pay for the markets for products. Technological advance was severely hampered by this fact. Urbanization in the western part of the empire was also minimal due to the poverty of the region. Slaves accounting for most of the means of industrial output, rather than technology.
See also 
- Livy, The History of Rome 21.63
- Safrai, Ze'ev (1994). The Economy of Roman Palestine. London: Routledge. p. 78. ISBN 0203204867.
- Grant, Mark (2000). Galen on Food and Diet. London: Routledge. p. 129. ISBN 0415232325.
- Cappers, R. T. J. (2006). Foodprints at Berenike: Archaeobotanical evidence of subsistence and trade in the Eastern desert of Egypt. Monograph 55. Los Angeles: Cotsen Institute of Archaeology UCLA. ISBN 1931745269.
- "Radio 4 - Unearthing Mysteries". BBC. Retrieved 2012-11-07.
- "South Asia | Search for India's ancient city". BBC News. 2006-06-11. Retrieved 2012-11-07.
- Haywood, John (2000). Historical atlas of the classical world, 500 BC–AD 600. Barnes & Noble Books. p. 46. ISBN 0-7607-1973-X. "Arikamedu was a trading port in the 1st century AD: many Roman artifacts have been excavated there."
- "Weilue: The Peoples of the West". Depts.washington.edu. 2004-05-23. Retrieved 2012-11-07.
- II Verr.V18
- Cato De.Agr 1.3
- Pliny NH 7.140
- Terrence 151
- Tacitus annas 4.13.2
- de.Agr. Praefatio
- Plutarch Cato the Elder 21.5ff
- Haywood, John (2000). Historical atlas of the classical world, 500 BC–AD 600. Barnes & Noble Books. p. 27. ISBN 0-7607-1973-X. "the empire's commercial classes remained small and enjoyed neither wealth nor the status of the landowning aristocracy...most production in the empire was small scale and under-capitalized, the rich preferring to invest in land. It is in any case doubtful, in view of the poverty of most of the empire's population, whether the markets existed to support a greater degree of industrial production. This is probably one of the factors behind the surprising lack of technological innovation in the empire...The ready availability of cheap slave labor may also have deterred investment in expensive machinery....But most of the west was too poor and under-populated to support this level of urbanization and towns remained primarily administrative or military centers."