In OTL Mount Athos is a self-governing monastic community that is part of Greece, best known for being exclusively male. It consists of some 20 principal monasteries (and a number of smaller ones and hermitaries), who elect a council, and occasionally come to blows (for reasons that often seem rather arcane to those outside the community). The only religious state is the Holy See.
In the Statelets timeline it is one of a larger number of such bodies, of varying formats, sometimes operating across state boundaries - having a greater presence than the religious bodies in OTL.
The most successful "foreign intervention" of the Mount Athos community is in negotiating a settlement between the various religious communities in Jeruasalem.