The island of Montecristo is a state nature reserve and forms part of the Tuscan Archipelago National Park.

Much of the island's fame is derived from the fact that it provides the setting for part of the novel The Count of Monte Cristo, by Alexandre Dumas.In the 19th century Alexandre Dumas was inspired by the island’s old St. Mamiliano monastery ruins and legends about pirates’ treasures buried here. 

Mamilian of Palermo spent time on Montecristo in the  fifth century, and constructed a monastery on the island.

Around the middle of the fifth century AD, the caves of the island became home to several hermits escaping from the Vandals of Genseric, the most important of whom was St. Mamilian.[1] They christened the island "Mons Christi", from which the modern name is derived. At the beginning of the seventh century, Pope Gregory the Great submitted them to the monastic rule of the Benedictines.[1] In this period, the Monastery of St. Mamilian was founded; as a result of donations to the Church, its wealth became legendary, and a chapel was built in the St. Mamiliano Cave where the saint had lived in the fifth century.[2] In 1216, the monks joined the order of the Camaldolese. Thanks to the donations of several noble families, the monastery became powerful and rich, and this gave rise to the legend of treasure hidden on the island.[1]

1.  "Timeline" (in Italian). Retrieved 27 February 2012.  archive.org
2. Peria, Gloria; Ferruzzi, Silvestre (2010). L'isola d'Elba e il culto di San Mamiliano(in Italian). Portoferraio.