The province of Terni (surface: 2.122 square kilometers) is on the southern edge of the Umbria region.
The most important natural elements in its landscape are: the complex river system; the woods, the olive-groves and the pastures. From a geological point of view, its territory is young and the morphology is generally rough, characterized by not very high peaks and long and narrow valleys.
The few plains are between mountains in the basins lacustral alluvial bottom and are drawn out among mountain slopes, which repeat their geographical orientation.

The river system is formed by the river Tevere and its tributaries, some of which (Nestore, Niccone and Paglia) are torrential streams, because of the lands impermeability. Another relevant tributary, the Nera, merges into the Tevere near to the provinces boundary of Viterbo, corresponding with the Marmore Falls (165 meters high).
The most important lake is the Pediluco Lake (surface 1,5 square kilometers, 19 meters deep), and the spas of the Acquasparta and Sangemini mineral waters are noted for their quality.

The territory of the province of Terni is populated widely. The urban network is traditionally organized on the ancient layout: an hierarchical polycentrism, which is dates back to the medieval age, when the principal centers were Orvieto (EAST) and Spoleto (WEST).
The industrial development of Terni, now the provincial capital, dates back to the end of the XIX century, when the urban factories of the previous century were replaced with the large scale chemical, iron and steel industries. The crisis of these big industries was partially checked when some years ago they were bought by international companies.

The recent urban growth has generated linear aggregations into the valleys and along the principal roads. A cluster of medium and small towns has been formed around Terni.
Since the middle of the last century the farm properties have been enlarged in the valleys, but in the mountains they remain small. Nowadays the sown fields prevails, but the hill landscape is characterized by vines, maples, elms and in the majority olive-groves, which are able to grow on the detrital soils.