The chief city in their territory was Heraclea Pontica, the inhabitants of which reduced the Mariandyni, for a time, to a state of servitude resembling that of the Cretan Mnoae, or the Thessalian Penestae.
According to modern researcher John Hind, "...the Mariandyni may have initially ceded some coastal territory [to the Heracleot colonists] fairly peacefully, being in need of protection from... the Bebrykes and the Paphlagones.
In time the Herakleots acquired the Lycus Valley as the basis of their prosperity, and the Mariandyni entered a form of collective serfdom in which the saving grace was that they could not be dispersed or sold abroad.
How this state of affairs was arrived at is not clear, but the people may have been sold into it at a time of weakness by their chieftains, or may have slowly descended into it as a result of "being protected out of all they owned" by the Herakleots...
The vigorous expansion of the Herakleot territory resulted in the locking of the Mariandyni into their agricultural villages as a dependent people, subject also to impressment as rowers in the fleet.