The Greek civilization developed around the 2nd millenium BC in the eastern part of the Mediterranean Sea: in the Balkan peninsula, the islands of the Aegean Sea and the coast of Asia Minor.
Greece was not a unified country. It was geographically and politically fragmented during most of its history.
However, it is considered a civilization as all the people living in that area had the same language, religion, customs...and they considered themselves members of the same culture.
Ancient Greece: Culture and Art
River Nile is the longest river in the world, around 7000 km long. It was essential to the development of the Egyptian civilization.