The Cascata delle Marmore is a controlled flow waterfall, among the highest in Europe, with a total difference in height of 165 m, divided into three jumps. It is located about 7.5 km away from Terni, in Umbria, almost at the end of Valnerina, the long valley carved by the river Nera. The name derives from the calcium salts present on the rocks that are similar to white marble. The waters of the waterfall are intensively exploited for the production of electricity, in the Galleto power plant. This means that the actual waterfall is not continuously working, but for most of the time it is reduced to the size of a stream. The basin of the Lake of Piediluco acts as a water reservoir for the power plant, built in 1929, capable of producing electricity with a capacity of about 530 MW. To adjust the functioning of the central unit and to allow it to be viewed at all, at defined times and periods, the cascade is operated at maximum flow: an acoustic signal warns of the opening of the regulating gates, and in a few minutes the flow increases up to maximum value. The waterfall is formed by the river Velino that, near the fraction of Marmore, flows from the lake of Piediluco and plunges into the underlying Nera gorge with a roar. The flora and fauna at the falls are typical of the Mediterranean scrub. However, unlike the Nera river park, there are rare or even unique species of birds in Italy. They are: The Dipper (it nests near the waterfalls on the Alps and on the Apennines, but in much higher altitudes than the Marmore Falls), the River Kingfisher (it is very rare to meet in Europe), Rondine montana, the solitary Sparrow ( it lives only close to the rocky and sunny walls), the White Dancer, the Yellow Dancer, the Common Kingfisher, the Nightingale, the Moorhen, the Mallard. The Velino river runs through a large part of the plateau that surrounds Rieti, but further downstream it is naturally disturbed by the presence of limestone massifs and the absence of an adequate bed where it flows; this particular geological configuration led, in the course of the eras, to the formation, in that stretch, of a stagnant swamp that was harmful to the healthiness of the places. In 271 BC, the Roman consul Manio Curio Dentato ordered the construction of a canal (the Cavo Curiano) to drain the stagnant waters in the direction of the natural jump of Marmore: from there, the water fell directly into the river Nera, tributary of the Tiber . However, the solution to this problem created another one: concurrently with the floods of the Velino, the enormous quantity of water transported by the Nera directly threatened the inhabited center of Terni. This was a reason for litigation between the two cities, so much so that in 54 BC. the question came directly to the Roman Senate: Rieti was represented by Cicero, Terni by Aulus Pompeo. The cause was resolved with nothingness, and things remained so for the following centuries. With the fall of the Western Roman Empire, the maintenance of the canal ended, which led to a decrease in the flow of water and a progressive swamping of the plain of Rieti. After various adventures, in 1422 a new canal was built to restore the original flow of the river (Cavo Reatino or Cavo Gregoriano, due to the intervention of Gregorio XII). Pope Paul III, in 1545, sent to Antonio da Sangallo the Younger to open another channel, Cava Paolina, but he managed to fulfill his task only for fifty years. It was then decided to expand the Cava Curiana and build a bridge, a sort of valve that would allow to regulate the outflow of water. This work was inaugurated in 1598 by Pope Clement VIII, who had entrusted the design task to Giovanni Fontana, Domenico's brother; obviously, the canal took the name of Cava Clementina. In the following two centuries, the work created many problems for the underlying plain, hindering the correct outflow of the Nera and causing flooding of the surrounding countryside. By order of Pope Pius VI, in 1787, the architect Andrea Vici worked directly on the leaps of the waterfall, giving it its current appearance and finally solving most of the problems. In the nineteenth century the waters of the waterfall began to be used for their driving force: in 1896, the newborn Acciaierie di Terni fed their mechanisms using 2 m³ of water from Cavo Curiano. In the following years, the waterfall began to be intensively exploited for the production of hydroelectric energy. On the origins of the waterfall there is a legend: a nymph named Nera fell in love with the beautiful shepherd shepherd but Juno, jealous of this love, transformed the nymph into a river, which took the name of Nera. Then Velino, not to lose his beloved, threw himself headlong from the cliff of Marmore. This jump, destined to be repeated for eternity, is now replicated in the Cascata delle Marmore.
De Marmore Falls dankt zijn naam aan de calciumzouten die op de rotsen aanwezig zijn en lijken op wit marmer.
Het is een waterval met gecontroleerde stroming en behoort tot de grootste van Europa; het water bestrijkt in totaal een val van 165 m (verdeeld in drie delen).