Poggio Mirteto is a comune (municipality) and former Catholic bishopric in Sabina in the Central Italian region Lazio (Latium). Administratively Poggio Mirteto is in the province of Rieti (formerly part of the province of Perugia) and geographically this municipality is about 45 kilometres (28 mi) northeast of Rome and about 20 kilometres (12 mi) southwest of Rieti.

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 (mirto in Italian and then the adjective Mirteto) 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 thirteenth century in an area around some earlier small castles: previously in this area there had been some old Roman villas. Later the town became part of Papal States.

On 6 and 7 July 1849 Giuseppe Garibaldi, during his retreat from Rome with about 4,000 troops and his wife Anita, stopped in Poggio Mirteto: in Poggio Mirteto's main square there is a commemorative plaque in the building where Anita, which was pregnant, stayed during these days.

In the end of the year 1860, similarly to other Papal States territories, Poggio Mirteto joined the Kingdom of Sardinia during the fast events which arranged the making of the Kingdom of Italy that happened in the next year. The then Special Commissioner for the Province of Umbria of the Kingdom of Sardinia, Gioacchino Napoleone Pepoli, created by decree the Province of Umbriaon 15 December 1860, merging the previous Districts of Perugia, Spoleto, Orvieto, Foligno, Terni and the one of Rieti; therefore Poggio Mirteto, which was in the Rieti District, was included in this new Province.

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