http://en.wikipedia.org/wiki/Mount_Athos

There is a prohibition on entry for women, called avaton (Άβατον) in Greek, to make living in celibacy easier for those who have chosen to do so.[18] Monks feel that the presence of women alters the social dynamics of the community and therefore slows their path towards spiritual enlightenment. The ban was officially proclaimed by the Byzantine emperor Constantine Monomachos, as a chrysobull, in 1046.[19]