Historical Overviews

Description of the Indian Ocean

The Indian Ocean touches Asia, Africa, Australia and Antarctica. It also connects and links the Continents called the Old World, in contrast to the New World, which is touched by the Atlantic, Pacific and Arctic Seas. The Indian Ocean covers 68,536,000 square kilometers (about 26 million square miles), which equals about a 20% of the world's ocean surface. It is the third largest of the world's oceans, according to the International Hydrographic Organization (IHO). The other four are the Pacific (155,600,000 square kilometers), the Atlantic (82,362,000 square kilometers), the Arctic Ocean (14,056,000 square kilometers), and the Great Southern Ocean (20,327,000 square kilometers). 

Note: Individual chapters for seven eras located at the bottom of this page.

Physical Geography 

 The shape of the Indian Ocean can be described as a huge letter 'M.' Its outline extends from the East African coast north to the Arabian Sea, down the western coast of India to Sri Lanka, and up India's eastern coast, where it forms the Bay of Bengal. The eastern arm of the M is formed by the Indochina Peninsula, the Island of Java, and the west coast of Australia. This letter M covers the area between the Tropic of Cancer in the Northern Hemisphere, past the Tropic of Capricorn in the Southern Hemisphere to the line of 40 degrees S latitude. According to the IHO and the United Nations Oceans Atlas, the area from 40 degrees S latitude to 60 degrees S latitude is included in the Indian Ocean. The area that encircles the globe from 60 degrees S latitude to the coast of Antarctica is called The Great Southern Ocean. The Indian Ocean’s width extends from 45 degrees E longitude to 110 degrees E longitude. 
The Indian Ocean region is larger than the geographic description of this body of water. The region includes coastlines of the Indian Ocean where people live who work on and from the sea. It also includes waterways that connect to the Indian Ocean and link important places where trade originated and distant ports where goods were carried. The larger region important to the story of the Indian Ocean includes three bodies of water in the west: the Arabian (Persian) Gulf, the Red Sea, and the Mediterranean, which linked Europe, Africa and Asia. In the east, the region includes thousands of islands east of the Strait of Malacca, the area between Southeast Asia and Australia that leads to the Pacific. The South China Sea is somewhat like the Mediterranean, because of its connection with East Asia, the source of many important products, migrating peoples, cultural influences and technologies that affected the Indian Ocean. 


The rim of the Indian Ocean that touches the continents of Asia, Africa and Australia lies mostly within the tropics. This means that all of the ports and bays on the ocean are free of ice all year round. There was no Ice Age in the Indian Ocean, so this zone was always habitable by human populations. The Ice Age affected the ocean in some ways, changing the amount of rainfall, the temperature, and especially, the shoreline. During the Ice Age, the huge island group in Southeast Asia was connected to mainland Asia, almost all the way to Australia. 
The Indian Ocean has a unique climate pattern based on seasonal exchange of air masses between land and sea. This pattern is called the monsoon, from the Arabic word mawsim. During summer, when the landmasses are warmed by the sun’s heat, air masses over the huge continent of Asia rise, pulling in air masses saturated with moisture from the Indian Ocean south of Asia.  The monsoon wind then blows from the southwest. During winter, the warmer air masses over the ocean pull in dry air masses from Asia, and the wind blows from the northeast. The tropical monsoon climate, combined with natural links across land and sea, made the Indian Ocean a place rich in plants and animals unique to this part of the world. Spices, tropical fruits, rare jungle animals, and sea creatures became rare and exotic products and natural resources that became valued items of trade, and material for real adventures, travel stories, and tall tales. 

How Historians Think Geographically 

Oceans are the opposite of landmasses in usual geographic thinking. Oceans have no landmarks like mountains, plains, valleys, and plateaus. For seafaring experts, of course, oceans have clear patterns that are not visible to landlubbers, such as winds, currents, and reefs. Historians study the story of human settlement and civilization, and so they focus on the land, terra firma. That is where farming, herding animals, cities, and towns are located. Historians have long studied rivers and inland seas as links, but oceans were thought of as barriers to people. The coastline was the edge of human existence. 
World historians have recently become more interested in the world’s oceans as connectors. There is plenty of evidence that people explored the seacoasts very early in human history, and that humans actually went to sea in rafts and boats to fish, and then to trade along the coasts. Even thousands of years ago, people were already sailing out into the oceans. As much as four thousand years ago, seafaring ships were large and strong enough to cross into the open oceans and navigation skills were advanced enough to bring them back to tell the tale. Another important quality of the oceans is that unlike territory that could be taken over and controlled by armies, it was much harder to control the coming and going of ships. Therefore, oceans have been freer zones of interaction than land regions. 
The evidence collected on each era of Indian Ocean history for this website illustrates a wide variety of interactions that took place during more than ten thousand years of human history, and a much longer prehistoric period. People migrated and traveled, traded and transferred ideas and technologies, engaged in warfare and peacemaking, spread religions and artistic ideas. Each era of history in the Indian Ocean was different. 
Read the short sections below as background to your exploration of each era’s map icons on The Indian Ocean in World History online resource. Under the heading and dates for each era, the reading describes what historians believe happened during each era, how interactions developed, how navigation technologies and routes changed, what groups and individuals played roles in the region, and what places were important then. Read what goods were produced and traded, and how cash and food crops were carried across the region over time. Learn about important ideas and belief systems that migrants, pilgrims, merchants, conquerors and ordinary people spread across the Indian Ocean lands. The readings also give clues to what historians do not know yet, and where they disagree about historical trends. 


For all of the time humans have lived in the Indian Ocean, with dramatic changes over time, some things have changed little. People still gather shells and fish in the ocean as they did at the dawn of time. Sailboats and coasting voyages for trade and transportation still take place among coastal people. Markets are still places where people come to exchange, whether they are online or on the beach. 

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