The Nera is the most important tributary of the Tiber; “it gives it to drink,” as the Italian proverb says, and rivals it in volume. It is formed by the junction of several streams descending from the Sibylline Mountains, Monte Velino, and the Sabine Hills. About two thousand years ago, it is said, most of these rivulets did not reach the Tiber; they were intercepted in the plain of Rieti, where they formed the Lacus Velinus, represented at the present day by a few ponds and marshes scattered over the fertile fields of the “Garden of Roses.” A breach effected in the calcareous rocks, and several times enlarged since, allowed the pent-up waters of the Velino to escape to the Nera, and in doing so they formed those beautiful cascades of Marmora, above Terni, whose charms have been celebrated by poets and painters. The river falls down a perpendicular height of {270} 542 feet in a single sheet, and then rushes down, over heaped-up blocks of rock, until it joins the more placid waters of the Nera. Far less grand, but perhaps {271} more charming, are the numerous cascatellas of the Anio, or Teverone, the last affluent of any importance which the Tiber receives above Rome. Standing on the verdant hill upon which is built the picturesque town of Tivoli, silvery cascades may be seen to escape in every direction. Some of them glide down the polished rocks; others shoot forth from gloomy arches, remain suspended an instant in the air, and then disappear again beneath the foliage; but every one of them, whether a powerful jet or a mere thread of water, possesses some charm of its own, and, as a whole, they form one of the most delightful spectacles to be witnessed in Italy. It is these cascades which have rendered Tivoli famous throughout the world; and in spite of the popular rhyme— “Tivoli di mal conforto, O piove, o tira vento, o suona a morto !”— {272} modern residences have taken the place of the villas of the ancient Romans, amongst which that of Hadrian was the most sumptuous. Its ruins, to the west of Tivoli, cover an area of three square miles. Recently it has been proposed to {273} utilise the great water power of the Anio far more extensively than has been done hitherto. The ancients contented themselves with quarrying the concretionary limestone, or travertin, deposited by the calcareous waters of the river, sometimes to the depth of a hundred feet. They made use of this stone for the construction of their public buildings. Travertin, when first quarried, is white; after a certain time it turns yellow, and subsequently assumes a beautiful roseate hue, which imparts a character of majesty to the edifices constructed of it. [Illustration: Fig. 99.—PEASANTS OF THE ROMAN CAMPAGNA.]