Roman commerce was a major sector of the Roman economy during the later generations of the Republic and throughout most of the imperial period. 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 and were part of its backbone. The Romans were businessmen, and the longevity of their empire was caused by their commercial trade.
Whereas in theory members of the Roman Senate and their sons were restricted when engaging in trade,Livy, The History of Rome 21.63 the members of the equestrian order were involved in businesses despite their upper-class values, which laid the emphasis on military pursuits and leisure activities. Plebeians and freedmen held shop or manned stalls at markets, and vast numbers of slaves did most of the hard work. The slaves were themselves also the subject of commercial transactions. Probably because of their high proportion in society compared to that in Classical Greece, the reality of runaways, and the 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, which used Roman numerals, was ideally suited to the counting of Roman currency and tallying of Roman measures.
Negotiatores, mercatores and pedlars
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. The argentarii acted as agents in public or private auctions, kept deposits of money for individuals, cashed cheques (prescriptiones) and served as moneychangers. In some instances the argentarii are considered a subset of the negotiatores and in others as a group apart. The argentarii sometimes did the same kind of work as the mensarii, who were public bankers appointed by the state. They kept strict books, called tabulae, which were treated as legal proof by the courts.
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. 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. These cities were connected by good roads. Navigable rivers were extensively used and some canals were dug, but neither leave such clear archaeological traces as roads. Consequently, they tend to be underestimated. Maintaining peace was a major factor in the expansion of trade. 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.
Recent archaeological and quantitative research has used coin-hoard evidence to examine the relationship between commercial infrastructure and monetary circulation in the Roman world. An analysis of georeferenced Republican coin hoards (155 BCE–2 CE) applied spatial interaction modelling to study how settlement hierarchies, transport routes, and urban infrastructure shaped patterns of circulation. The study found that coin finds were concentrated around major urban and transport nodes, including Rome, principal roads, and coastal port systems, suggesting that commercial infrastructure helped structure the spatial integration of the Roman economy.
By the 1st century, the provinces of the Roman Empire were trading huge volumes of commodities to one another via 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 remains. Very exceptionally, as at Berenice, there is evidence of long-distance trade in black pepper, almonds, hazelnuts, stone pine cones, walnuts, coconuts, apricots and peaches besides the more expected figs, raisins and dates. 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 Roman 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 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.
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 – with most land trade moving by pack mule – 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 liburna galleys and triremes of the Roman navy.
Bulky, low-value commodities, like grain and construction materials, were traded only by sea routes, since the cost of sea transportation was sixty 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, Leukos LimenYoung, Gary K. - "Rome's Eastern Trade: International Commerce and Imperial Policy 31 BC - AD 305" - Ed. Routledge, (2003) , 9781134547937 p. 35-48 and Myos Hormos on the Red Sea coast of Roman Egypt to the ports of Muziris and Nelkynda in the 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 circa 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 Alexander the Great had conquered as far as India, and the Roman god Bacchus was also said to have journeyed there. The Far East, like sub-Saharan Africa, was a mysterious land to the Romans.
India
There was an Indian in Augustus's retinue (Plut. Alex. 69.9), and he received embassies from India (Res Gestae, 31); one which met him in Spain in 25 BC, and one at Samos in 20 BC.
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 on the Malabar coast. 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 Greek Periplus of the Erythraean Sea. In Latin texts, the term Indians (Indi) designated all Asians, Indian and beyond.
The main articles imported from 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. 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 one of the trade centers.
Pomponius Mela argued for the existence of Northeast Passage through the northward strait out of the Caspian Sea (which in Antiquity was usually thought to be open to Oceanus in the north). Book III, Chapter 5 , copied by Pliny the Elder.
China