 In June 2006, the only "comunes" with a population over 10,000 were Terni, Orvieto, Narni and Amelia.It is bordered to the north with the Province of Perugia, to the east, south and west with the Lazio (Province of Rieti and Province of Viterbo) and to north-west with the Tuscany (Province of Siena).The province extends into the south-west of the Umbria region, occupying the last section of the Nera River valley near the confluence with the Velino River, and the eastern part of the valley of the Tiber River.