While it is true that the variations of ancient Greek religion and its practice were in many ways each unique to its era, culture, and region it is also true that that religion could change when one of those factors changed. Here I want to talk a bit about how religion could change when its practitioners moved from one place to another.
As in later centuries, for the ancient Greeks, growth and expansion often meant the colonization* of new places, places where the new inhabitants no longer had a strong historical attachment to and identification with the region. And that’s significant, because in any ancient community, the issue of How We Got Here was a crucial one. The Athenians were famously autochthonous–in other words, “we’ve just always been here.” Cities without this advantage might have a particular founder, often a historical or mythical figure associated with the city and its residents. In any case, there would be a story that placed them where they lived, giving them not only a community narrative but a right and a reason to be there.
A colony’s story would have not only a founder (oikistes) but a mother city as well; the mother city would be the origin of the colony’s religious and other practices. If you lived in a colony of Athens, your religious practice, at least initially, would be very much Athenian. Your religious calendar, the gods you worshipped, the festivals you observed, all would be based on the practices of Athens. Unsurprisingly, there would typically be the addition of a hero-cult in the new colony for the founder himself. The new city thus had a share in the prestige of the mother city. The close mother-colony relationship was marked by the establishment of the colony’s hearthfire from flames taken from the hearth of the mother city.
The new hero-cult for the founder would be the first religious difference between the colony and the mother city, but other differences would eventually come about as well. This was natural as the colonists started to think of themselves less as, say, Athenians and more as citizens of the new city. As the new self-identification took hold (and as the practical differences between the old and the new region became apparent) some religious practices would be changed and others added, while others perhaps became less important or were, over time, gradually eliminated.
If there were existing cults in the region, these might or might not be maintained but, if kept, seem to have been considered secondary to the new imports, at least initially.
If, for example, the mother city was coastal and the colony inland, the imported cult of Poseidon might well be reduced in importance over time.
If the new city was very near an excellent source of iron ore and subsequently became a great center of metalwork, a cult of Hephaistos might well become a more central part of the city’s religious calendar.
A great plague and its subsequent relief could generate a new cult in gratitude for that salvation (as is said to have been the case with the cult of Apollo Smintheus in Hamaxitus).
New arrivals to the new city might bring along their own gods and cults–which, again, might or might not be adopted by the city as a whole.
And in some cases, a new cult could be begun by an individual who had had a religious experience and could promote the new god’s worship by others in some way.
* Note: The act of colonization was generally justified by the colonists’ belief that it was the will of the gods, specifically Apollo (a will determined, typically, by consulting an oracle); the existence of and need for this justification is at least a recognition of the idea that taking land occupied by others was Not A Nice Thing.
For futher reading:
Garland, Robert. Introducing New Gods: The Politics of Athenian Religion. Cornell University Press: New York, 1992.
Malkin, Irad. “Religion and the Founders of the Greek Colonies.” Diss, University of Pennsylvania, 1981.