When we think of colonization, we generally think of states making organised efforts to appropriate overseas territory by force, creating a periphery whose labour and natural resources are exploited for the benefit of the colonizing centre. Greek colonization was very different. Indeed, prominent scholars have argued that the word is entirely inappropriate, and we would increase people's understanding of the phenomenon if we stopped calling it that.^1
The most obvious point is that the word is anachronistic. The word "colony" and its cognates are derived from the Latin colonia, a military settlement intended to serve as an outpost and garrison of Roman power anchoring newly conquered territory. No such word exists in Archaic Greek and the so-called "Age of Colonization" (mainly the 8th and 7th centuries BC) predates its use by hundreds of years. Instead, Greeks referred to overseas settlements as apoikiai (literally "away-from-homes") and to the process as apoikismos ("moving away from home"). You'll notice that these terms are a lot less value-laden; they imply little more than settlements created by migrants, without any built-in sense of a power structure or of claims to conquered territory.
This is indeed perhaps the main difference between Greek settlement overseas and the processes of the Age of Colonization. While modern colonization is all about appropriation and exploitation for the sake of a remote colonizer, Greek apoikiai were not conquests, but autonomous communities. In the Archaic period, they owed neither tribute nor fealty to their metropolis (mother city). While they might retain similar cults and customs, and often paid ritual homage to their founders, they were free to pursue whatever policy they saw fit and were under no obligation to transfer any of their wealth back to the places they had left behind. On this point alone, it is clear that Greek "colonies" were not colonies; they were new but not inferior or subordinate communities. Their autonomy allowed some to rise to great prominence with no notable effect on their metropoleis. Settlements like Sybaris and Tarentum in Southern Italy, and Syracuse and Akragas in Sicily, became renowned for their great wealth and size, rivalling or even surpassing the states of Old Greece. Many of them became metropoleis in turn, sending out second-generation settlements, which might also send out their own settlements, until opportunities ran out.
Indeed, Greek overseas settlements were detached from their mother cities in more than just a geopolitical sense. While individual communities in Old Greece often took the initiative to found a new settlement, and presumably provided a core group of settlers, the process of apoikismos was far less of an official state-sanctioned act than the word "colonization" implies. In the Early Archaic period, the states of Greece had seen only very limited institutional development, and it was simply not possible for any of them to control or manage an overseas empire. Instead, it appears that a colonizing venture was begun when either a state or a private person put out a call for volunteers, who might then gather from far and wide to have a share in the undertaking. This is the only way we can justify places like Phokaia, Eretria and Miletos allegedly founding dozens of overseas settlements without completely exhausting their own population. As the poet Archilochos observed, when the men of Paros settled on Thasos in the Northern Aegean:
The misery of all the Greeks has rushed to Thasos.
In other words, the process was not driven by states looking to expand, but by individuals and groups hoping to build a new life, with or without the sanction of a mother city. Often the more important sanction sought was actually that of the Oracle of Apollo at Delphi, which played a key role in assigning the direction of overseas settlement and is the likely source of many surviving colonization stories. As for the ventures themselves, some were prompted by a search for trade contacts, land, or specific resources like metals and timber; others by political exiles' need for a new home; others by local emergencies such as drought, famine, or displacement through war.
The earliest overseas settlements seem to have grown out of settling groups of traders, only a minority of whom would even be Greek. Pythekoussai, on Ischai in the Bay of Naples, is the earliest one (settled c. 770 BC) - and is identified as one of the possible places of contact where the Greeks may have learned their alphabet from the Phoenicians. The earliest "proper" apoikiai, meanwhile, like Megara Hyblaia on Sicily, show clear archaeological evidence of the presence of a range of different groups of Greeks and local populations. The most likely process of such early "colonization" was the arrival of a mixed group of Greek opportunists in a new land, in which they either forced out or found some way to live together with the people already present. In some cases the indigenous population was subjected and turned into rural slaves; in others, they formed distinct groups inhabiting their own parts of the new settlement, fading gradually into the Greek settlement through intermarriage and the adoption of foreign wares and habits.
The result of these processes of mingling and assimilation, both within the collective "Greek" settling population and between Greeks and local peoples, was that each overseas settlement's laws and religious practices were a mixture of things brought from home and things adapted to the local situation. Apoikiai provided an opportunity to create a community out of whole cloth, and while some traditions were copied from the mother city, others were drafted specifically to fit the need. Places like Megara Hyblaia and Metapontion are the earliest Greek urban centres laid out to a regular grid plan, with a space left open specifically to meet and conduct public and private business. Some of the earliest attested lawgivers, semi-mythical authors of states' customs and systems of government, operated in Sicily and Southern Italy rather than in Greece itself. Often new cities would copy each other, rather than simply adopting the laws of the mother city. Settlements that founded their own apoikiai might create 'families' of overseas Greek states, which spoke the same dialect and shared customs and religious cults. These states would then try to participate in panhellenic festivals, games and rituals in their own right, establishing their place as autonomous communities in the Greek world, and feeding back to Old Greece the ways in which they had organised their societies.
It is only in the Classical period that Greek practices of overseas settlement change. This is the time when old mother cities start to stake a claim to honour and special treatment from their 'children'; when Greeks of the same dialect groups begin to assert a form of kinship that had never been an issue in the mixed communities settled across the Mediterranean and the Black Sea; and when new overseas settlement takes on a very different, more imperialist character.
In the years between the 8th and 5th centuries BC, Greek states grew tremendously in size and complexity, and by the beginning of the Classical period the larger states had developed the ability to maintain and control far-flung domains composed of home territory, planted settlements, allies and subjugated communities. As a result, they began to see the value of overseas settlements as outposts of their sphere of influence, rather than simply as an escape valve for unwanted elements in society. In the Classical period, when states like Athens or Sparta found new cities elsewhere, it is understood that these cities are not wholly independent; they are extensions of the mother city, meant to represent its interests abroad. These places are intended to safeguard strategic positions, replace local populations, and assert the authority of imperialist states. The cities Athens planted in Thrace (Nine Ways, Amphipolis, Brea) were intended to give Athens ready access to the timber and mines of the area. Sparta's settlement of Herakleia in Trachis gave it an excuse to arrange the affairs of Central Greece as it saw fit. While the Corinthian settlements of Potidaia and Kerkyra were not of Classical date, the role they played in triggering the Peloponnesian War was much to do with Corinth appropriating these old daughter cities in the Classical way, demanding that its rights as a mother city were respected and using the opportunity to support those regarded as kinsmen in struggles to protect Corinth's interests. This is "colonization" of a kind we might recognise more easily, and one more worthy of its bloodsoaked modern name.