Indo-Gangetic Plain

• 1. Introduction

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  The Indo-Gangetic Plain stretches 700,000 square kilometres across the northern and north-eastern reaches of the Indian subcontinent, a single unbroken apron of soil that holds nearly one-seventh of all the people on Earth. It runs from the foot of the Himalayas southward to the Vindhyas, from North East India westward to the Iranian border. That is a staggering sweep of territory, and yet what makes it truly remarkable is what lies beneath every field and city built upon it: the world's largest expanse of uninterrupted alluvium, deposited grain by grain by the Indus, the Ganges, and the Brahmaputra over an almost incomprehensible span of time.

  People have sensed this richness for millennia. By 3000 BCE the Indus Valley Civilisation had already taken root here. Every major empire that rose across this part of the world chose this plain as its political and demographic heart. The questions worth sitting with are simple: how did this landscape come to be, what has it meant to the peoples who inhabit it, and why does it remain, even today, one of the most densely populated and intensely farmed regions anywhere on the planet? The answers begin deep underground, in rocks that predate the Himalayas themselves.

• 2. How the Plain Was Born

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  Darashaw Wadia believed the depression underlying the plain was a furrow that had existed since the plateau to the south and the mountains to the north first took shape. Edward Suess offered a different picture: a vast syncline formed when the southward advance of the Himalayas was blocked by the ancient Indian landmass. Sydney Burrard went further still, arguing the region was a deep rift in the Earth's crust that was later filled with alluvium, and he pointed to other rift valleys in the Himalayan and Deccan Plateau regions as supporting evidence. Ferdinand Hayden and Richard Oldham pushed back hard, finding no evidence for such a large rift and considering it geologically impossible.

  More recent research has settled on a different account. Sediment that once lay at the bed of the prehistoric Tethys Sea folded northward as the Indian plate drifted in that direction, and a trough formed later when the Himalayas emerged. Over ages, the Indus, Ganges, and Brahmaputra filled that trough with silt. Beneath all that accumulated sediment, the plain rests on hard crystalline rocks that tie the Himalayan region to the peninsula to the south. The result of all this slow accumulation is the world's largest unbroken sheet of alluvium, a foundation that would prove extraordinarily generous to everything built upon it.

• 3. Four Strips of Land

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  Running south from the Himalayas, the plain resolves into four distinct strips, each with its own character. The first, called the Bhabar, sits immediately below the Himalayan foothills. It is a narrow, highly porous band largely composed of stones and rocks carried down by rivers. Most streams that enter the Bhabar simply vanish underground.

  The Terai lies next. Here the rivers that disappeared in the Bhabar reappear, depositing new silt and creating a zone that receives heavy rains for most of the year. Thick, wet evergreen vegetation covers much of it. Below that comes the Bangar, the broad fertile belt of older alluvium that forms the core of the flood plains, with laterite deposits mixed into its soils. At the southern edge lies the Khadir, low-lying ground composed of the newest silt carried down from the upper plain by rivers still running hard. Each strip is a different chapter in the same long story of rivers building land from the inside out, and together they explain why the Ganges-Brahmaputra Delta at the far eastern end is the largest river delta in the world, spreading across more than 100,000 square kilometres into the Bay of Bengal.

• 4. Empires of the Plain

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  In 3000 BCE the Indus Valley Civilisation established what would become one of the earliest human settlements in the subcontinent. The Vedic period that followed, running from roughly 1500 to 600 BCE, gave the region one of its oldest recorded names: Aryavarta, meaning Land of the Aryans. The Manusmriti defines Aryavarta precisely as the tract between the Himalaya and the Vindhya ranges, from the Bay of Bengal to the Arabian Sea.

  The Maurya Empire, which existed from the 4th to the 2nd century BCE, unified most of the subcontinent into a single state and remains the largest empire ever to exist on Indian soil. Its demographic and political centre lay squarely in this plain. The Kushan Empire expanded out of what is now Afghanistan into the northwest of the subcontinent in the middle of the 1st century CE, a period when maritime trade along the Silk Road was also flourishing. The Gupta period, from the 4th to the 7th century CE, is remembered for achievements in arts, architecture, and science, again anchored here.

  In 1191 CE, the Rajput king Prithviraj Chauhan unified several Rajput states and defeated the invading army of Shihabuddin Ghori at the First Battle of Tarain. Ghori came back, won the Second Battle of Tarain, and the Delhi Sultanate rose in the 13th century CE. Then in 1526 CE, Babur swept across the Khyber Pass and founded the Mughal Empire, which held the plain for nearly three centuries. The Maratha Empire, founded by Chatrapati Shivaji, briefly captured the region in the early 18th century. Ranjit Singh established the Sikh Empire in the north-western part around the same time. The English East India Company's victories at the Battle of Plassey in 1757 and the Battle of Buxar in 1764 consolidated British power in the lower Gangetic plain, and with the eventual defeat of the Marathas, the entire region passed under the British Raj until Indian Independence in 1947.

• 5. Water, Crops, and Climate

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  Rainfall across the plain is anything but uniform. The eastern portions receive the heaviest annual totals, and during the monsoon after summer they frequently flood. Moving westward, rainfall thins steadily until the landscape transitions into the Thar Desert. Yet the northernmost strip of the plain, running along the Himalayan foothills, receives about 50 inches of rainfall a year, keeping it green.

  That gradient shapes what farmers grow. Rice dominates the wetter east and north, while wheat, barley, and millet are the main crops in the drier west. The seasonal Luni River and streams like it support only limited agriculture across the Rajasthan Plain, much of which is covered by the Thar Desert, stretching 650 kilometres across 200,000 square kilometres. The Sindh Plains in Pakistan, by contrast, receive roughly 13 inches of rain annually, mostly between June and September, and the economy there rests heavily on agriculture. The Indus Delta, where the river meets the Arabian Sea, has received significantly less water since the 1940s because large-scale irrigation works upstream now capture much of the Indus flow before it reaches the coast. The delta is home to the largest arid mangrove forests in the world.

• 6. The Delta at the Edge

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  The Ganges-Brahmaputra Delta is where the plain makes its final statement. Spread across Bangladesh and the Indian state of West Bengal, it covers more than 100,000 square kilometres, with roughly two-thirds of that area lying in Bangladesh. From the Hooghly River in the west to the Meghna River in the east, the delta stretches about 260 kilometres. More than 130 million people live here, making it one of the most densely populated places in the world.

  The delta is also one of the most fertile regions of the entire plain, a product of the same silt-building process that shaped every strip northward. Agriculture and fishing form the backbone of its economy. The cost of living at the confluence of so much river water and ocean is exposure to heavy tropical cyclones, which strike the region with regularity. That combination of extraordinary fertility and recurring catastrophe has defined life in the delta for as long as people have been here, and the population of more than 130 million shows that the draw of the land consistently outweighs its dangers.