these led to writing, according to denise schmandt-besserat, professor of mid-eastern studies. schmandt-besserat: each of these shapes was meaningful. the cone probably stood for a unit of grain, a small unit of grain. the disc probably for an even larger unit of grain. one animal -- and one animal meaning in the middle east one goat or one sheep. so how do the tokens lead to writing ? well, it took a long time. keach: it took nearly 4,000 years. but around 3500 b.c., in a culture known as sumer, the world's first cities emerged. now, a more complex economy required more complex record-keeping. accountants took a ball of clay which they poked inside with the fingers to make a cavity. you know, it's just like a tennis ball of clay or even smaller. and once they had a good cavity, they would put inside tokens, and then a flap would be put on top, and all of this was closed. and we are in pre-writing time. and at that time every sumerian had a seal. and when the stone is pressed onto the surface of the envelope, it leaves then a design which is then the mark of the person or the a