The Fanum Voltumnae (‘shrine of Voltumna’) was the chief sanctuary of the Etruscans; fanum means a sacred place, a much broader notion than a single temple. Numerous sources refer to a league of the “Twelve Peoples” (lucumonies) of Etruria, formed for religious purposes but evidently having some political functions. The Etruscan league of twelve city-states met annually at the Fanum, located in a place chosen as omphalos (sacred navel), the geographical and spiritual centre of the whole Etruscan nation. Each spring political and religious leaders from the cities would meet to discuss military campaigns and civic affairs and pray to their common gods. Chief amongst these was Voltumna (or Veltha), possibly state god of the Etruria.
Roman historian Titus Livius mentioned the Fanum Voltumnae five times in his works and indicated “…apud Volsinios…” as the place where the shrine was located. Modern historians have been looking for the Fanum since at least the 15th century but the exact location of the shrine is still unknown
Source: Fanum Voltumnae – Wikipedia