Another hypothesis suggests that the federal shrine of the Etruscans was located to the northern coast of Lake Bolsena, in a place known as "Civita di Grotte di Castro", a plain area close to the church of San Giovanni in Val di Lago (currently in the commune of San Lorenzo Nuovo). This hypothesis (also supported by Luigi Catena) comes out of another study based on the so-called "Rescritto di Spello" (Rescript of Hispellum) issued by emperor Constantine I in a date between 333 and 337 AD to authorize the Umbrians' annual celebration: