Imagine yourself high in the air over the Himalayas. Look down and you see a forbidding landscape of snow-capped mountains and harsh vegetation. But now look to the south-east and discover an immense floodplain stretching between the mountains and the sea. That shimmering green expanse is Bangladesh.

You may well wonder why a book about Bangladesh should begin with the Himalayas. There is a good reason: without the Himalayas, Bangladesh would not exist. In a sense, Bangladesh is the Himalayas, flattened out. Every spring the mountain snow melts and the icy water sweeps along particles of soil, forming into rivers that rush to the sea. As these rivers reach the lowlands, they slow down and deposit those particles, building up a delta. This age-old process has created the territory that we now know as Bangladesh – a territory that pushes back the sea a little further with every annual deposit of new silt.

The delta is huge because almost all water running off the Himalayas, the highest mountain range on earth, has to pass through it (Map 1.1). On the southern side numerous rivulets and rivers run together to form the mighty Ganges that flows eastwards through India for hundreds of kilometres before it enters western Bangladesh, where it is also known as the Padma. On the northern side of the Himalayas an equally majestic river, the Brahmaputra (or Tsangpo), forms in Tibet.