The physical conformation of Central Italy compelled its inhabitants to turn their attention at an early period to the construction of drains and other hydraulic works. Considerable artificial channels were rendered necessary in order to regulate the flow of the Arno and Tiber in the neighbourhood of Chiusi. In southern Etruria, the district now known as the pestilent Maremma, could only have been rendered healthy by systematic artificial drainage. The sites of Populonia, Saturnia, Cosa, Veii, and Cære were thus rendered habitable and fertile, and a great part of Latium Maritimum, the Pomptine marshes, and the tract about Suessa Pometia must have been artificially and skilfully drained at the time of the greatest prosperity of those places. Many of the ancient cities of Central Italy had tunnels bored underneath their streets which served as thoroughfares connecting the different parts of the city, or as secret passages leading out into the country. Such tunnels are found at Præneste and Alba Fucensis. An account of the attempted escape of Marius from Præneste, by means of the tunnels, is given by Velleius. The catacombs show that the same genius for tunnelling operations existed at a later time among the Italians of the empire. [Sidenote: Alban Mount.] The triumphal route by which the festal processions from Rome ascended the Alban Mount diverged from the Appian road at the ninth milestone. It probably passed by Marino to Palazzuolo and thence ascended to the summit by a series of zigzags. The stones which mark its course have the letters N V. (numinis via) cut upon them. On the summit stood the Temple of Jupiter Latiaris, the ancient sanctuary of the Latin league. The sole remains of this famous building are now built into the wall of the reservoir of the convent of Palazzuolo. They consist of fragments only. Most of the stones employed by Cardinal York in 1783 in the erection of the convent of Palazzuolo and the church of the Trinity, on the site of the temple, were taken from the ruins, but nothing can be learnt from them regarding the ancient buildings. The summit of the hill is not broad enough to have supported any large building, and we may therefore conclude that the temple was of small size, and that the great festival games at the Feriæ Latinæ were held in the Prati d’Annibale below. The inscriptions on some of the stones are merely the freaks of some modern stonemasons. The fragments which remain were probably used for the area round the temple. [Illustration: Plan of the Area OF THE TEMPLE of JUPITER ON MONTE CAVO]