The Aegean Sea
The Greeks were protected on one side by mountains, and on the other side by the waters of the Aegean Sea. The coastline of the Balkan Peninsula where the Greek mainland is found is made of thousands of inlets and coves. These coves were ideal for sea ports. Because no part of Greece was more than fifty miles from the coastline, many Greeks made their living through trade, fishing, and other sea faring means.
The mountains of the Balkan Peninsula made travel over land difficult. This tended to isolate cities and states from one another. As a result, the nation of Greece never united under one central government, but instead was comprised of smaller regions known as city-states, each with its own local government.