I saw this a while back and meant to get to it earlier, but Livescience is running a series of articles on some rather significant events in human history, the second being the development of writing. This generally occured with the development of urban life as a way of keeping track of property. The beginning of writing forms the divide between pre-history and history.
The first evidence we have of writing is from ancient Mesopotamia, starting around 3000 BC, when priest began keep agricultural records, beginning with pictograms and then developing into a system of standard symbols they used to mark clay tablets with a reed stylus, a type of writing called cuneiform. The system later developed as a way of representing sounds in addition to numbers. The Egyptian system of hieroglyphics is thought to have developed soon thereafter.
"A few thousand years later, as variations on the two systems spread throughout the region, the entire ancient world had writing schemes that vastly improved the efficiency of economies, the accountability of governments and, maybe most importantly to us, our understanding of the past."
It should be pointed out that only a very few people were literate in those times, and actually quite far into the modern period literacy was the almost exclusive preserve of aristocratic males. Almost 20% of people residing on the Third World nations today is still illiterate.