When the Sea Took Half the World

Twenty-one thousand years ago the map of the world was very different to the one that pertains today. Massive ice sheets covered where London, Manhattan, northern China and Japan now stand. So much of the planet’s water was locked into that ice, that the seas lay about a hundred and twenty metres lower than today. The equatorial world by contrast to the frozen north was warm, fertile and had all the people, but a great part of the coastal areas of that equatorial world now lies on the sea bed.

At the centre was the Indian subcontinent, hinged at the middle of the Indian Ocean between Africa, Arabia and Southeast Asia. Around 12,000 BC the world was warming and the glaciers were melting. It happened relatively quickly, although interrupted by a colder spell from 10,900 to 9,700 BC which is called the Younger Dryas. Thereafter the temperature was relatively stable, about two degrees Celsius warmer than today. This abrupt change in temperature caused three massive floods around 12,000 BC, 9,500 BC and 5,600 BC. The last was remembered worldwide in legends and stories which included the Biblical Flood.

Off Southeast Asia lay Sundaland, named after the Sunda Shelf, which joined today’s Indonesia and Malaysia into a single broad peninsula reaching from Indochina toward Borneo. To the north stretched another land, called Mudalu or Mu in legends. It bridged southern Japan to Okinawa and the Ryukyu Islands toward Taiwan and encompassed the coastal areas off south China. An area the size of India stood above the waves and much of it, we can infer, was just as densely inhabited as the Indian subcontinent at the time. When the ice melted, roughly twenty-five million square kilometres of habitable land was drowned, a loss larger than the whole of modern Europe.

These warm coasts were the busiest places on earth, because the estuaries, deltas and river mouths were the fertile areas of the world, where game, cereals, nuts and vegetables were plentiful, where men could fish, where the timber grew for boats, and where traded goods could be gathered. The geneticist Stephen Oppenheimer has argued that Sundaland led the Neolithic revolution, with grinding stones for wild cereals in use in the Solomon Islands some twenty-six thousand years ago and yam and taro under cultivation in Indonesia around 10000-15000 BC. Root crops were grown in the New Guinea highlands from around 9000 BC. On his reading, the knowledge travelled west from there toward India. The shared words for rice-growing among the Munda peoples of central India and the languages of Indochina are part of the evidence it left. The outward migration from the subcontinent that seeded much of the ancient world is an argument I have made separately.

Off south-west Okinawa divers have identified eight submerged megalithic structures under thirteen metres of water, including rock circles, a square platform, stone streets, flights of stairs and cut archways. Three hundred miles south at Yonaguni sits a five-stepped stone terrace 182 metres wide and 27 metres high, in thirty metres of water, apparently modified from the natural rock. How much of that is human-made and how much natural is still debated. What is irrefutable, however, is that people were living on these shelves before the sea took them.

They were at home next to and on deep water. Australia was reached by boat more than sixty thousand years ago, the Americas forty thousand, which means open-ocean crossing, even if sailing from island to island, was among the oldest skills the human race possessed, older by tens of thousands of years than farming or writing.

On the Horton Plains of Sri Lanka there are traces of people managing crops of barley and oats as early as fifteen thousand years ago, with herding and settled grain farming in place by 8000 BC. Cotton and hemp were under cultivation in the northwest of the Indian subcontinent soon afterwards, and the cloth was already traded into the Persian Gulf while much of Europe still lived by hunting and gathering. The bull was tamed and honoured as the animal that pulled the cart, turned the press and provided precious fertiliser. That reverence never lapsed.

By around 7000 BC the inland town of Mehrgarh, in the hills of Baluchistan, had grown into a cluster of villages spread across dozens of hectares, growing wheat, barley and cotton, drilling beads of turquoise and lapis, and producing the earliest cotton thread yet found anywhere on earth. The archaeologist Jim Shaffer has argued that the northwest of the subcontinent shows an unbroken cultural tradition reaching back to at least 8000 BC. Mehrgarh is what survives on dry land, well inland from the coast. The coastal towns of the same age, which by every rule of trade and settlement would have been larger and richer, went under with the water.

The outstanding feature that sets the subcontinent apart is continuity, and it runs deeper than pottery styles. The painted rock shelters at Bhimbetka reach as much as thirty thousand years old, and looking at the dancing deity there, with his bangles and his trident, the historian Michael Wood found it difficult to separate the image from the dancing Shiva sold on pilgrim posters in India today. At a fourteen-thousand-year-old site archaeologists lifted a carved yoni stone, an image of the female generative organ, and the villagers nearby recognised it at once as something still in use. Across the country hundreds of temples hold, by local tradition, that the present building is a rebuilding of a far older one on the same sacred ground.

In most of the world, such threads were cut long ago, by conquest, migration and the imposition of new gods. In India, despite Muslim invasions, they held. India’s oldest memories recorded in its voluminous ancient literature, should be treated as serious historical documents.

The melting of the ice did one more thing across the north of the subcontinent. It made an extraordinary set of rivers. The retreating Himalayan glaciers fed the Indus, the Drishadvati, the Yamuna, and above all the Sarasvati, which ran between two and five miles wide in places and dwarfed the Indus. Together they carved a drainage network known as the Sapta Sindhu (Land of Seven Rivers) that watered valleys where wheat and barley were probably being grown before 9000 BC.

The scale of what grew out of that watering is breathtaking. By the third millennium BC this river system fed roughly 3,800 villages, towns and sizeable cities including important ports, in total about a million and a half square miles from Afghanistan to Maharashtra. Contemporary Egypt covered thirteen thousand square miles. Sumer was smaller still. The full case for displacing Mesopotamia from its usual place at the head of the story is one I have made separately. By one widely cited estimate the Indus-Sarasvati network at its height housed a tenth of the world’s population. This gave it huge economic power. We know from 19th century Britain and 20th-21st century America, that this gives huge cultural influence too.

Global warming weakened the ice sheets over Hudson Bay and James Bay until the enormous meltwater lakes behind them found routes to the sea. Each collapse fed further warming through the ocean’s currents. The Younger Dryas reversal, when the world dropped back into near-glacial conditions for roughly twelve hundred years, ended around 9,700 BC with warming that resumed at almost violent speed, and the second of the three great meltwater surges followed close behind. The mainstream explanation for this reversal is a disruption of the North Atlantic circulation caused by an earlier meltwater pulse. A more contentious one, developed by Firestone, West and Warwick and popularised by Graham Hancock, argues for a comet or comet-fragment airburst over the northern ice sheets, based on peaks of platinum, iridium and nanodiamonds found in a layer at that depth across dozens of North American sites. Most archaeologists remain sceptical, on the grounds that the geochemical signature is patchier than the hypothesis implies. My feeling, developed in the book and in writing on black-swan events of prehistory, is that the latter is strong enough to keep the case open. Around thirty-five species of North American megafauna disappeared across this same window, mammoths and mastodons among them, and gradual warming does not usually kill on that scale.

But whatever the trigger, the ice let go. What it took with it, in three great surges, was the busier half of the world.

The warmth that built this world unmade a great part of it. The sea came back in three great surges, around 12000, 9500 and 5600 BC. Each collapse sent tsunamis racing across the oceans. The third and last was the one the coastal peoples remembered for the rest of their history. It filled the Black Sea, the Baltic, the Yellow Sea and the Persian Gulf, and finished the drowning of Sundaland, leaving it as the Indonesian islands and the present east Asian coast. To feel the scale, set it beside the Indian Ocean tsunami of 2004, far smaller than any of these, which still took more than a quarter of a million lives in an afternoon.

The people who survived climbed to high ground and carried the memory forward, and the pattern of those memories is itself an argument. Almost every culture on earth keeps a story of a great flood. They cluster most thickly in exactly the regions that drowned, around the old Sundaland shore, where the tales describe the sea rising, rather than the rain falling, and escaping onto high ground rather than into an ark. In the south of India, the Tamils still speak of a lost homeland called Kumari Kandam, which once reached beyond Sri Lanka toward the Maldives. In the north the memory took the form of Manu, warned of the coming water, building a boat that Vishnu, in the shape of a great fish, towed to safety. Taken together these are the scattered recollections of a single event, remembered differently by the peoples the water drove apart.

The Indian coast has its own record, told first as legend and slowly confirmed by divers. At Mahabalipuram in Tamil Nadu, local tradition speaks of Seven Pagodas, of which the present Shore Temple is the last, the other six taken by the sea. The British traveller John Goldingham wrote the story down in 1798. Two centuries later a set of structures was found offshore, a mile out and covering several square miles of sea floor, and while some are recently drowned due to tsunamis, those further out are still to be properly excavated.

Off the Konkan coast in Maharashtra, in only three to six metres of water, sits a wall of huge Deccan rock twenty-four kilometres long, nearly three metres high and two and a half wide, dated to around six thousand BC. Beside it, over sixty rock sculptures of a mother goddess, birds and animals, dated between 7000 and 4000 BC. Rocks moved, cut and placed on that scale imply an organised society working the coast for a very long time.

The most contested case is the Gulf of Cambay, where in the early 2000s sonar and dredging identified what appears to be a drowned port on the banks of an ancient river with right angled streets and walled structures on the sea floor. Organic samples returned dates well before the last flood. Mainstream archaeology was sceptical because the material had to be dredged rather than excavated in place, due to the silt-laden waters being unfit for diving and the dating of dredged wood is not the dating of a building. My own reading, developed in the book, is that the sonar images and the ancient literary record together are strong enough that the site deserves the full excavation it has never yet had, and the sheer quantity of dredged up materiel indicates a substantial, long-lasting settlement well into the Ice Age. The Sumerian temples which appear so abruptly after the Flood may well be modelled on drowned predecessors on this coast, connected by a trade route running from the Gulf of Cambay to the head of the Persian Gulf.

Since 2019, 25 kilometers off Poompuhar at the then mouth of the River Cauvery, maritime archaeologists from Bharathidasan University have found an eleven by three kilometre-wide area containing a drowned harbour, dockyards, settlements and walls linked by canals up to 250 metres wide, able to handle 70-80 ships at once which the research team dates to about 13,000 BC. The initial date needs checking but this is much easier to research than the clouded waters of Cambay.

The Sri Lankan chronicles also record the floods. The Rajavali, compiled from earlier accounts by fourth-century Buddhist monks, records three great deluges swallowing thousands of towns and villages up to twenty miles inland, and describes a citadel of Ravana lost to the sea before the earliest of them. Tamil tradition dates the destruction of the first Sangam at Tenmadurai to around 9,600 BC, remarkably close to the modern dating of the second meltwater surge. None of these on their own is absolute proof. Together however, they are a persuasive pattern.

The work is picking up again. A respected archaeological team has in 2025 and 2026 surveyed underwater, off the modern town of Dwarka in Gujarat. The fact that they went back after the 2025 season suggests interesting finds although they have not published yet. In September and October 2025 the Tamil Nadu State Department of Archaeology, working with the Indian Maritime University, ran the first phase of a new underwater survey between Poompuhar and Nagapattinam, reaching depths of twenty-three metres, with a second phase to follow using side-scan sonar, magnetometers and three-dimensional seabed mapping in partnership with the National Institute of Ocean Technology and the National Institute of Oceanography. The Tamil Nadu government committed seven crore rupees to the project in its 2025-26 budget. Poompuhar sits over the port the Tamil epics call Puhar, described in the Silappadikaram and the Manimekhalai as a place of foreign goods, gold and pearls that “sank into the cruel sea,” and earlier surveys in the 1980s by S. R. Rao had already discovered submerged structures from that stretch of coast. Whether the current work reaches only the Sangam-era layers or eventually the older strata beneath is not yet clear. But four years after my book was published, India is committing serious money to the search for its maritime origins.

Re-order the evidence in this way and the shape and story of the ancient world begins to rewrite itself. When the ice melted and the sea settled into its modern outline, the north of the planet was still thinly-peopled. The subcontinent already had the climate, rivers, farms, cities, ports, ships and the crowded population, along with a biodiversity matched only by Africa, Southeast Asia and equatorial South America. Each of those other regions had a part of the advantage but Africa never built the long-distance sea trade or the cities to organise it. The Austronesian seafarers who reached the Americas were kept there by the very winds and currents that had carried them. India lost much less land than Sundaland, due to its steeper coastal shelf, although it lost some pioneering ports, according to its ancient literature. But it kept its memory intact and its habit of recording what it knew unbroken.

The Rig Veda dating to before 4500 BC with knowledge back to before 7000 BC, describes ships with a hundred oars, three-masted vessels, outriggers and cargoes of sixty tons, prayers said before a voyage, and merchants who crowd the great waters with ships, an indication of convoys of ships, perhaps. The first 3-masted ship in the Mediterranean by contrast is recorded in a document of 1406 AD. In ancient India, at the end of the Ice Age, the gods had already been named, the ships were already at sea.

From the subcontinent, the story of the ancient world flowed outward.

This essay is drawn from my own book, How Maritime Trade and the Indian Subcontinent Shaped the World (Pen & Sword, 2021), and the sources it discusses. On the drowned lands of Southeast Asia and the case for their early sophistication, see Stephen Oppenheimer, Eden in the East: The Drowned Continent of Southeast Asia (1998). On Indian cultural continuity, see the archaeological work of Jim G. Shaffer and Michael Wood’s The Story of India (2007). On the Sri Lankan highland cereal evidence, see the palynological work of Rathnasiri Premathilake on the Horton Plains. On the offshore structures at Mahabalipuram and the recording of the Seven Pagodas tradition, see John Goldingham’s 1798 account and the more recent National Institute of Ocean Technology surveys. On the Gulf of Cambay findings and the debate around them, see the discussion and citations in my own book. On the 2025 first-phase underwater survey off Poompuhar, see the reporting in The South First and India Beyond Curry, October 2025, and the Tamil Nadu State Department of Archaeology’s own announcements. On the Younger Dryas Impact Hypothesis, see R. B. Firestone et al., Proceedings of the National Academy of Sciences (2007), and the updated formulation in Wolbach et al., “Extraordinary Biomass-Burning Episode and Impact Winter Triggered by the Younger Dryas Cosmic Impact ~12,800 Years Ago,” Journal of Geology (2018); I discuss the black-swan events of prehistory at greater length in my own Substack essay “Cataclysms of Antiquity” (2025). The story of Manu and the fish is told in the Shatapatha Brahmana and the Matsya Purana.

This essay is drawn from my three-volume history of maritime trade. The books are available on Amazon, via Garuda in India, Pen & Sword in the UK.