Mount Athos is a mountain and a peninsula in Macedonia, northern Greece, called Άγιο Όρος (Ayio Oros or "Holy Mountain") in Modern Greek, or Ἅγιον Ὄρος (Hagion Oros) in Classical Greek. It is home to 20 Orthodox monasteries and forms an autonomous state under Greek sovereignty. Only monks are allowed to live on Athos and the current population numbers around 1,400. The peninsula, the easternmost "leg" of the larger Chalkidiki peninsula, protrudes into the Aegean Sea for some 60 km at a width between 7 to 12 km and covers an area of about 390 km², with the actual mountain and its steep, densely forested slopes reaching up to 2,033 m.
The seas around the end of the peninsula can be dangerous. Xerxes I had a channel excavated across the isthmus to allow the passage of his invasion fleet in 483 BC.
Monastics from Mount Athos are often referred to as Athonites or Hagiorites.
Mount Athos as a monastic community was formally founded in 963, when St. Athanasius (not to be confused with the 4th century St. Athanasius the Great) established the monastery of Great Lavra, still the largest and most prominent of the 20 monasteries. It enjoyed the protection of the emperors of the Eastern Roman Empire during the following centuries and its wealth and possessions grew considerably. The Fourth Crusade in the 13th century brought new Roman Catholic overlords which forced the monks to seek protection from Pope Innocent III, until the restoration of the Byzantine Empire. It was raided by Catalan mercenaries in the 14th century, a century that also saw the theological conflict over the hesychasm practised on Mount Athos and defended by Gregory Palamas.
The Byzantine Empire collapsed in the 15th century and the newly established Islamic Ottoman Empire took over. They heavily taxed the monasteries, but for the most part left them alone. The population of monks and their wealth declined over the next centuries, but was revitalised around the 19th century by the donations and new arrivals from other Orthodox countries, such as Russia, Bulgaria, Romania and Serbia, while each country came to exert its influence on individual monasteries. In 1912, during the First Balkan War, the Ottomans were forced out and after a brief conflict between Greece and Russia over sovereignty, the peninsula formally came under Greek sovereignty after World War I.
Politically the peninsula is mostly self-governed and consists of 20 main monasteries and the capital city and administrative centre, Karyes, also home to a governor as the representative of the Greek state. Beyond the monasteries there are 12 sketae, smaller communities of monks, as well as many (solitary) hermitages throughout the peninsula. Visits to the peninsula are possible for laymen, but they need special permission.
Women are completely barred from the peninsula, a fact which has earned a certain amount of fame; even female domestic animals (with the exception, some say, of cats, as well as chickens which lay eggs that provide the fresh egg yolk needed for the paint used in iconography) are forbidden. However, during the Greek Civil War, Athos did shelter refugees including women and girls. 
In modern times, the Mount Athos monasteries have repeatedly been struck by wildfires, e.g. in August 1990, and in March 2004, fire gutted a large section of the Serbian monastery, Chilandari. Due to the secluded locations of the monasteries, often atop small hills, as well as the unavailability of suitable fire fighting gear, the damages inflicted by these fires are often considerable.
Greek is commonly used in all Greek monasteries, but in some monasteries there are other languages in use, in St. Panteleimon, Russian; in Chilandari, Serbian; in Zographou, Bulgarian; and in the sketae of Prodromou and Lacu, Romanian. Today, many of the Greek monks can also understand English or other European languages.
List of Monasteries and Sketes
World Heritage Classification, UNESCO
- Date of Inscription - 1988
- Reference No. 454
- Criteria: (i), (ii), (iv), (v), (vi) and (vii)
- An Orthodox spiritual centre since 1054, Mount Athos has enjoyed an autonomous statute since Byzantine times. The 'Holy Mountain', which is forbidden to women and children, is also a recognized artistic site. The layout of the monasteries (about 20 of which are presently inhabited by some 1,400 monks) had an influence as far afield as Russia, and its school of painting influenced the history of Orthodox art. 
- United Nations - Copyright © 1992-2008 UNESCO World Heritage Centre
-  A Pilgrim's Guide to Mount Athos
- Mount Athos Monasteries
- Greece Mount Athos
- The Holy Mountain - Mount Athos: The Heart of Orthodox Monasticism
- Mount Athos: The Holy Mountain
- Walk in Mount Athos
- Chilandar Monastery
- The Friends of Mount Athos
- A Pilgrim's Guide to Mount Athos (courtesy of The Friends of Mount Athos)
- Books of Athonite Interest (courtesy of The Friends of Mount Athos)
- Visiting Mount Athos
- An American Pilgrim on Mount Athos
- Visiting Athos, the Holy Mountain (Aghion Oros)
- The Holy Mountain
- Mount Athos
- Athos - Monastic life on the Holy Mountain (exhibition)
- Byzantine Monastic Foundation Documents. Dumbarton Oaks Research Library and Collection.