Within Lake Bolsena, the Bisentina island (commune of Capodimonte) is also regarded as a sacred isle of the Etruscans, possible site for the Fanum, and gate to the underground world of Agharti. A sanctuary located on an island not situated at the sea would have been accessible to priests and kings of the 12 cities (with their closest entourages), their protection being granted during the religious and political meetings by a handful of armed men. An Italian television program Voyager (1 October 2003) supported this hypothesis, suggesting for the Etruscans a parallelism to the Incas populations, who had also chosen one of Lake Titicaca’s islands as their omphalos.
Indeed, not only the Incas but, for the same reasons, various peoples have decided to erect their most eminent sanctuary on sacred islands: the Egyptians at Philae; the Greeks at Delos; the Germans at Helgoland in the North Sea and on the island of the goddess Nerthus, in the Baltic; the Celts at Gavrinis, near to the Breton coast in France, at Iona in Scotland, etc. This hypothesis finds a type of confirmation in the poem the Theogony, by the Greek oral poet Hesiod (8th-7th century BC) : “They ruled over the famous Tyrenians, very far off in a recess of the holy islands”.
Source: Fanum Voltumnae – Wikipedia