MOUNT ATHOS, the easternmost of the three prongs of the peninsula of Chalkidiké, has been for centuries the "Holy Mountain" of the Orthodox Church. Pious, or at least penitent, Byzantine, Trapezuntine, Serbian and Russian Emperors and dignitaries founded twenty monasteries there in the dark centuries; more than one monarch sought refuge there from the intrigues of courts, and, to make the solitude safer, it has always been a rule that no female -- except the inevitable female flea, which invades most Eastern monasteries -- should set foot upon Mount Athos.