What is known today as "Ancient Greece" is a very important period in history. Most people agree that it came after the Minoan and Mycenaean civilizations. It ended when the Romans invaded Greece, in 146 BC. Greek culture had a very powerful influence on later civilizations, especially the Romans. The Greeks developed what is now called a city-state, or a polis. There were many polises. Some of the more important ones were Athens, Sparta, Corinth and Thebes. The word "politics" comes from there. It literally means: things that are about the polis. Greek cities did not have much contact with each other, because of the mountains and many islands Greece is made up of. When a city no longer had enough food to care for all its citizens, some people were sent out to set up a new city. This was called a "colony". Each city was independent, and ruled by someone within that city. Colonies also looked to the city where they originally came from for guidance.