So you know how stone age people lived thousands of years ago? They lived in small groups in caves. As time passed( talking about few million years ) people started to live in large well organized groups to form a town or a city. Such a group is called civilization. People in same civilization work together. They often have same traditions, language, arts, architecture.

Civilizations in olden times often got formed along the river, so that the people could farm on the fertile banks of the river.

One of the oldest civilizations of the world was in India called the Indus Valley Civilization, along river Indus. There were two main cities that formed in this civilization. They were Harappa and Mohenjo-Daro,about 400 kilometers away. The people of these cities lived in stone houses two and three stories high. They had sewage systems and mostly did farming.

Other oldest civilizations of the world that existed almost around same time as Indus Valley Civilization are:

Mesopotamia –  existed between two mighty rivers,the Tigris and the Euphrates, in the part of the world we now call the Middle East.
Ancient Egypt – existed along the banks of the Nile River in Egypt, Africa.
Did you know?
There are tribes even in these times that live like ancient man. They live in their own small groups in jungles and do not want any contact with outsiders. Therefore, they are still uncivilized. One such example is Jarawa tribe of Andaman and Nicobar Islands.