BC, Sparta began to build a series of alliances with other Greek states, which became the Peloponnesian League: by 550, cities such as Elis, Corinth, and Megara were part of the alliance. This series of alliances had the dual purpose of preventing the cities of the League from supporting the Helot population of Messenia, and of helping Sparta in its conflict with Argos, which in the archaic period was along with Sparta one of the major powers in the Peloponnese. Colonization In the eighth and seventh centuries BC, Greeks began to spread across the Mediterranean, the Sea of Marmara, and the Black Sea. This was not simply for trade, but also to found settlements. These Greek colonies were not, as Roman colonies were, dependent on their mother-city, but were independent city-states in their own right. Greeks settled outside of Greece in two distinct ways. The first was in permanent settlements founded by Greeks, which formed as independent poleis. The second form was in what historians refer to as emporia; trading posts which were occupied by both Greeks and non-Greeks and which were primarily concerned with the manufacture and sale of goods. Examples of this latter type of settlement are found at Al Mina in the east and Pithekoussai in the west. The earliest Greek colonies were on Sicily. Many of these were founded by people from Chalcis, but other Greek states, such as Corinth and Megara were also responsible for early colonies in the area. By the end of the eighth century BC, Greek settlements in southern Italy were also well established. In the seventh century, Greek colonists expanded the areas that they settled. In the west, colonies were founded as far afield as Marseilles. In the east, the north Aegean, the Sea of Marmara, and the Black Sea all saw colonies founded. The dominant coloniser in these parts was Miletus. At the same time, early colonies such as Syracuse and Megara Hyblaea began to themselves establish colonies. In the west, Sicily and southern Italy were some of the largest recipients of Greek colonisers. So many Greek settlements were founded in southern Italy that it was known in antiquity as Magna Graecia – "Great Greece". In the last quarter of the eighth century, new Greek settlements were founded in Sicily and southern Italy at an average rate of one every other year, and Greek colonists continued to found cities in