Besides these offshoots of the Apennines there are in this part of Central Italy several detached mountains, rising almost like islands on the seashore, of which the two most remarkable are the Monte Argentaro on the coast of Tuscany near Orbetello (2087 ft.) and the Monte Circello (1771 ft.) at the angle of the Pontine Marshes, by the whole breadth of which it is separated from the Volscian Apennines.
The lakes of Bolsena (Vulsiniensis), of Bracciano (Sabatinus), of Vico (Ciminus), of Albano (Albanus), of Nemi (Nemorensis), and other smaller lakes belong to this district; while between its south-west extremity and Monte Circello the Pontine Marshes form a broad strip of alluvial soil infested by malaria.
He was employed by Napoleon to superintend the engineering operations for protecting the province of Ferrara against the inundations of the Po and for draining and improving the Pontine Marshes.
He was an active patron of agriculture and commerce: he even interested himself in the draining of the Pontine marshes.
The district sloping down from Velletri to the dead level of the Pontine (Pomptine) Marshes has not, like the western and northern slopes of the Alban Hills, drainage towards the Tiber.
Cuniculus, Emissarium, and the same author's Chapitre d'histoire Pontine (Paris, 1889).
Satricum, on the other hand, was certainly south of the Alban Hills, between Velitrae and Antium; while Cora, Norba and Setia (all of which retain their ancient names with little modification) crowned the rocky heights which form advanced posts from the Volscian mountains towards the Pontine Marshes.
Suessa Pometia also, on the borders of the Pontine Marshes, to which it was said to have given name, was a city of importance, the destruction of which was ascribed to Tarquinius Superbus.
To him no doubt is due the direct line of road through the Pontine Marshes from Velitrae to Terracina.
The Pontine Marshes (q.v.) included in the latter division, were drained, according to the plan of Bolognini, by Pius VI., who restored the ancient Via Appia to traffic; but though they have returned to pasture and cultivation, their insalubrity is still notorious.
Berti, Paludi pontine (Rome, 1884); R.
De la Blarchere, Un Chapitre d'histoire pontine (Paris, 1889).
Or repairs to the Quirinal, Lateran and Vatican palaces; the erection of four obelisks, including that in the piazza of St Peter's; the opening of six streets; the restoration of the aqueduct of Severus ("Acqua Felice"); besides numerous roads and bridges, an attempt to drain the Pontine marshes, and the encouragement of agriculture and manufacture.