Take a look at this monsoon chart, paying special attention to the western Indian Ocean between the east coast of Africa and the west coast of India, and you might notice a pattern:

The left chart depicts the prevailing winds in the Indian Ocean in February; the right, in August. In winter, a sea of arrows representing the northeast monsoon blows south down the coasts of Arabia and Africa from India and Persia. In summer and fall, the winds reverse course, returning up the coast to the north Indian Ocean.

Compiling the results of “16,914 separate observations,” the U.S. Navy Bureau of Ordnance and Hydrography published the comprehensive monsoon chart in 1859. In the description, Superintendent of the U.S. Naval Observatory Matthew Fontaine Maury wrote “The winds of this Ocean undergo such great, so many, and such regular changes according to the seasons, that it has been found very difficult to map them.” Despite the complex and sometimes fickle nature of the Indian Ocean monsoons, what Maury’s Bureau was observing and documenting was a phenomenon that had been known – and used – for centuries by mariners and traders from Mozambique to Malaysia, and which had facilitated rich economic and cultural exchange between the societies around its rim.

Aided by the seasonal pattern of the monsoon winds, merchants from India, Persia, Arabia, and East Africa have sailed the Indian Ocean since prehistoric times. Long-distance trade around the western Indian Ocean occurred in antiquity and is first mentioned in written sources in the Periplus of the Erythraean Sea, a Greco-Roman description of the coasts from the Red Sea to the west coast of India which dates to the early 1st millennium CE. The golden age of Indian Ocean trade arose in the 8th century, around the beginning of the Abbasid Caliphate. Arab and Persian sailors, traveling in ships called dhows, brought goods and Islam to far-flung port cities. These cities – many on islands which provided sheltered bays for docking – played host to merchants trading in ivory, gold, timber, ambergris, Chinese and Islamic ceramics, and enslaved Africans.

In East Africa, a common culture and important trade language developed along what became known as the Swahili coast, where several important city-states thrived. The important 1572 German-Flemish atlas of the world’s cities, Civitates orbis terrarvm, included views of three Swahili coast cities: Mombasa (today Kenya’s second-largest city), Kilwa, and Sofala. Other notable Indian Ocean cities in the atlas include Aden in modern Yemen and Diu and Goa in western India.

This period lasted until the late 15th century, when European commercial networks, even as they stretched westward across the Atlantic, expanded into the Indian Ocean. Portuguese, Dutch, and English traders established economic and military outposts along the coasts of Africa and Asia, tapping especially into the lucrative spice trade. The map below from the Miller Atlas, created for King Manuel I of Portugal in 1519, shows a sea full of ships flying Portuguese and Ottoman flags. The ornately-decorated atlas was the product of Portuguese cartographers and a Dutch miniaturist.

At first the Portuguese continued the tradition of focusing trade at coastal cities, and established a network of forts from East Africa to Southeast Asia to protect their commercial interests. Soon, however, traders and prospectors were lured into the interior of southeast Africa by their desire to control the region’s gold trade. Several gold mines can be seen on this 1630 map of the area around the Zambezi River, part of an atlas of Portuguese trading settlements by João Teixeira Albernaz:

Two of the older Swahili cities mentioned above, Kilwa (Quiloa) and Sofala, also appear on the Teixeira map. Although the East African coast was split up between several European colonial powers – Portugal, Britain, and Germany – into the 20th century, the Swahili language remains a major language and important lingua franca throughout East Africa today.

Learn more:

• View Swahili arts across the Indian Ocean in this online exhibit from the Smithsonian National Museum of African Art.
• Examine 20th-century photos of East Africa’s Swahili Coast in this blog post from 4 Corners of the World.
• Explore the debated identity of Taprobana, a mysterious Indian Ocean island, in this blog post from Worlds Revealed.
• Find more Library of Congress resources about the regions involved in Indian Ocean trade in the African and Middle Eastern and Asian Divisions.