纪录片《大英博物馆世界简史》 013印度封印（6）

"All culture stems from that early moment, all civil society stems from that and, in some ways, things have not changed as much as we would think - a house is still a house, the public domain or government building is still the same, a person sits on the stoop or step, he faces the sun or away from the sun. There's a relationship between the private domain and public domain; so all those things are really there - and the beginning of government is there too. We pride ourselves in being on one level very different but, actually, we're very close to those people."

We could get even closer if only we could read the writing on our seal, and others like it. Above all, the animal images on the seals are a series of symbols - one looks like an oval shield; others look like matchstick human figures; there are some single lines, and there's a standing spear shape. But what are they? Numbers, logos, symbols - or are they in fact a language? We don't know. Since the early 1900s, people have been trying to decipher them - nowadays of course using computers - but we just don't have enough material to go on.

The seals are often pierced, so they may have been worn by their owners, and they were probably used to stamp goods for trading - they've been found in Iraq, Iran, Afghanistan and central Asia.

So, we have a vast network of complex organised cities with flourishing trading links to the world beyond, all thriving between 3000 and 2000 BC. And then, around 1900 BC, it all comes to an end. The cities turned to mounds of earth, and even the memory of this, one of the great early urban cultures of the world, appears to have vanished. Why? Possibly the need for timber to have fired the brick kilns of the huge building industry may have led to extensive deforestation. More importantly, climate change seems to have caused tributaries of the Indus to change course or to dry up completely.