The settlement of Castro was founded in prehistoric times, and was later the seat of an unspecified Etruscan city, probably Statonia.
In 1527 a pro-independence faction assumed power, but they were later ousted by Pier Luigi Farnese, whose family was to rule Castro until the 17th century.
The town, which in the meantime had been reduced to "gypsies' huts" (in the words of a contemporary), was reconstructed according to the design of Antonio da Sangallo the Younger.
The Farnese and the papacy fought a stalemate war and the Pope agreed to treaty terms only months before his death in 1644.
[1][2] No longer a residential bishopric, Castro (Castrum in Latin) is today listed by the Catholic Church as a titular see.