 According to Giuseppe Marocco's 1833 book  the name Poggio Mirteto means the "knoll with plenty of Myrtus plants" because in its territory there would be plenty of Myrtus plants (called "mirto" in Italian, which is where the adjective "mirteto" comes from) and the old town was built on a knoll which in Italian is translated with the toponym Poggio.Poggio Mirteto's cathedral, formerly seat of its own bishops, became the episcopal see of the Bishop of the Suburbicarian Diocese of Sabina-Poggio Mirteto.Poggio Mirteto was founded in the early 13th century in an area around some earlier small castles