Sumer was the first city developed it was developed around 3,500 B.C.E.
During the old stone age, people were hunters and gathers, they were nomads, they used stone and bone tools group were no more then 20-60 people.
The new stone age/ Neolithic Era began about 9,000 B.C.E when farming was developed. This was the time we started domesticating animals we have today. The nomadic period ended in this time too. The population increased because people had more food to feed bigger families. Some farming villages even turned into cities.
In some areas of the world people had a dramatic shift in their way life; the development of civilization. These places started the development of writing, government, job specialization and increased technology improvements.