A wind that changes direction
In the northern Indian Ocean the prevailing winds reverse with the seasons. From roughly June to September the southwest monsoon blows from Africa and Arabia toward India. From about November to March, a milder northeast wind blows the other way. Sailors who understood these monsoon trade winds could plan a round trip around them, outbound in summer and home in winter, rather than fighting the wind.
Ships had probably been using coastal routes in this region for a very long time, and the Indus cities had sea links with Mesopotamia in the Bronze Age. What changed in the late centuries BCE and the early centuries CE was the scale and regularity of direct voyages between Egypt and India, which were connected with the Roman takeover of Egypt in 30 BCE.
Hippalus and the “discovery” of the winds
A tradition recorded by Greek and Roman writers credits a pilot named Hippalus with discovering the direct route across open water. Some writers also named the southwest wind after him. The tradition is hard to date or verify. Many scholars think the winds were already known to Arab, Indian and Egyptian sailors, and that Hippalus, if he existed, brought the knowledge into Greek-language sailing practice. It is safer to say that the Greek-Roman world learned to use the open-sea route during the last centuries BCE and that it was well established by the first century CE.
The route
Ships started from Red Sea harbours on the Egyptian coast, notably Berenike and Myos Hormos, which were linked to the Nile by desert roads. Goods came down the Nile to Koptos, then travelled overland by caravan to the coast, because sailing in the northern Red Sea was slow and difficult. Excavations at Berenike have found Indian items there, such as pepper and pottery, as well as evidence of a cosmopolitan community.
From the Red Sea, ships sailed down to the Arabian coast and then, with the southwest monsoon behind them, crossed to western India in a matter of weeks. Our general picture of ancient seafaring suggests ships were small and sailed mostly in daylight where possible, yet monsoon crossings were direct and fast compared with coastal routes. The return voyage took the northeast wind in winter.
Ports in India
The chief Indian destinations were on the western coast. The Periplus of the Erythraean Sea, a Greek merchant’s guide written in the first century CE by an unknown author, lists ports and goods. It names Barygaza (modern Bharuch) in the northwest and Muziris on the Malabar coast in the south, and it describes what could be bought and sold in each. Arikamedu, on the southeast coast, was another place with Mediterranean pottery and trade links.
The exact site of Muziris is still discussed, and excavations at Pattanam in Kerala have been proposed as connected with it, though this is debated. The Periplus is a valuable source, but the author’s knowledge was unequal, so some details may be less reliable than others.
What was traded
From India and further east the ships carried black pepper, which was a favourite in Roman cooking, along with pearls, gemstones, ivory, cotton textiles, and spices such as malabathrum, a leaf used in perfume. Some silk passed through India as well. Our article on the Silk Road trade routes describes the overland side of that business. Exchanges with Arabia also touched the incense trade.
In the other direction, Roman merchants carried coined gold and silver, wine, olive oil, glass, coral and metals. Roman coins, mostly silver denarii of the early empire, have been found in southern India, often in hoards. The Periplus lists Roman exports, but not their quantities.
One striking document is the so-called Muziris papyrus, a second-century CE Greek text found in Egypt. It appears to record a loan secured against cargo on a ship called the Hermapollon, bringing goods from Muziris. The papyrus gives a sense of high-value cargoes and the financing involved, though its details are complicated and still under study. For general background on such loans see ancient banking.
Concerns about the drain of coin
Roman writers sometimes complained about the cost. Pliny the Elder wrote that India and neighbouring peoples drew a large sum of money from the empire each year, and gave figures of tens of millions of sesterces. These numbers are rhetoric as much as accounting, and the exact amount cannot be checked. What they show is that Romans of the first century CE knew the trade was large and that luxury goods were a topic of public worry.
Why the trade mattered
Trade across the monsoon route linked the economies of the Mediterranean and South Asia, and gave profits to merchants, shipowners, port towns and the Roman treasury through customs duties. Indian rulers also benefited from taxes and trade. Greek and Indian words, ideas and people moved with the goods.
The trade shrank or changed in later centuries, with disruption in the Roman world and shifts in the Red Sea route, but the monsoon pattern itself remained a basis of Indian Ocean commerce long afterwards. The seasonal winds were a natural feature that people learned, over generations, to turn into a reliable schedule.