I'm going to continue in a similar vein with another myth set in Sparta, not a myth about
Sparta. Don't worry, I'll get there.
When the Spartans descended on the Peloponnesus, they brought more than just their sky gods with them. They brought the whole pantheon.
Apollo's twin sister Artemis, the virgin goddess of the hunt, was popular with the Spartans. She was the protector of girls and in Sparta that protection extended to the youths as well. However, she developed a darker aspect here than elsewhere in the world.
When the Dorian's conquered Lacedaemonia, they found a wooden post-like idol of Artemis already present in a willow thicket. This idol became known as Artemis Orthia. Once again, most scholars agree that an older goddess, Orthia was supplanted by the conquering goddess Artemis.
(Lacedaemonia is the name for the land that the Dorians conquered. The Dorian invaders became known as Lacedaemonians or Spartans.)
The idol, known as a xoanon, was a malevolent, nonhuman wooden effigy. Legend says, Spartans from the surrounding four villages quarreled while making sacrifices to Artemis Orthia. Most of the Spartans were killed in the ensuing fight and the remainder died of disease. Whether because of the idol's influence or because a miasma fell upon them due to their blood-guilt is unclear.
Following this, an oracle proclaimed that Orthia's altar must be stained with human blood and human sacrifices by lot were established. When asked why Sparta didn't just follow the practices of the Skythoi (Scythians) and sacrifice captives to the goddess, Apollonius said, "It is not congenial to any of the Greeks to adopt in their full rigor the manners and customs of barbarians (non-Greeks)."
When Lycurgus the lawgiver came to power in Sparta, he altered the custom. The sacrifices were abolished, but to slake the goddess' thirst for blood the youths of Sparta were flogged until they bled. An ordeal known as the Diamastigosis.
This rite of passage was so popular that an amphitheater was constructed for the audience. During the Roman times the ritual became little more than a blood spectacle that sometimes ended in the death of the young men, coming full circle in a return to human sacrifice. Showing the modern myth that the future is more progressive isn't always the truth.
This is an instance of what is called a "survival", where a former deity, ritual or cult is absorbed into the new reigning deity's sphere. Sometimes only the portions that fit with the new deity's identity are absorbed piecemeal, other times they are engulfed whole. Thus "converting" the followers of the previous god. Or would it be more correct to say subverting the newcomers?