Clinging almost impossibly to a sheer cliff in northern Greece, the Monastery of Simonos Petra, transcends country-based branches of the Christian faith, embracing monks from across the world. The monastery is one of 20 in the autonomous all-male monastic community of Mount Athos, known in Greek as Agion Oros, or Holy Mountain. (AP video by Srdjan Nedeljkovic. Drone shots by Thanassis Stavrakis. Production by Costas Kantouris and Theodora Tongas)