In the remains of these ancient Aqueducts, some are elevated above the ground upon a solid mass of stone work, or upon arches continued and raised one above the other ; other portions are subterraneous, passing through deep excavations, and in many instances piercing through mountains of rock ;

such is that seen at Vicovaro beyond Tivoli, where a tunnel of about five feet deep and four broad, pierces a rock for a distance of more than a mile.

These Aqueducts were generally built of stone and covered by arches or large flat stones. At certain distances

vents were provided to discharge the water from the channelway ; and cavities were formed, into which the water was precipitated, and where it remained till its mud was deposited, and ponds in which it might purify itself

One of these Aqueducts was formed with two channels, one above the other : they were, however, constructed at different periods; the most elevated was supplied by the waters of the Tiverone, Anio novus, and the lower one by the Claudian water. It is represented by Pliny, as the

most beautiful of all that had been built for the use of Rome. It was begun by Caligula, and finished by Claudius, who brought its waters from two springs called Coeruleus and Curtius. Vespian, Titus, Marcus - Aurelius, and Antonius Pius, repaired and extended it ; it is now called Aqua, Felice.

The Aqueduct that conveyed the Aqua Neroniana to Rome, was built of brick this, as well as the former, was ;