There was not a single "Greek Empire" that existed throughout history. Ancient Greece was a civilization that flourished from the 8th century BC to the 6th century BC. This period was characterized by the rise of independent city-states, such as Athens, Sparta, and Thebes. The conquests of Alexander the Great in the 4th century BC created a vast empire that stretched from Greece to India. This empire eventually fragmented, and Greece came under the rule of the Roman Empire.