146 SECTIONAL ADDRESSES. 
The gorge has, alas, lost much of its picturesque character owing to 
the construction of a large reservoir for the channel which supplies the 
electric-power works at Castel Madama, some three miles further down. 
At the lower end of it the Aqua Claudia divides into two branches, the 
slits for the sluices being still clearly visible at the point of junction. The 
original line kept along the left bank until it reached Vicovaro, where it 
crossed the Anio by a bridge which was repaired by Hadrian, and is still 
in use as a road-bridge ; but at a later period, probably that of Hadrian 
also, a branch was constructed. The channel first descended by a slope 
of 1 in 4°6, or 217-4 per 1,000, and then crossed the Anio by a bridge, of 
which scanty remains are preserved. The Marcia crossed the river a little 
further down, by a bridge of which hardly anything remains, and that 
little belongs to the Imperial period. 
The intake of the Anio Vetus was situated, not above or in the gorge 
of S. Cosimato, as was hitherto believed, but 35-50 metres above the 
bridge at Vicovaro, where we saw and levelled in 1915 the crown of the 
concrete arch of the channel. In 1925 nothing was to be seen; but there 
are remains of the channel, built in volcanic tufa, and belonging quite 
possibly to the original construction, on both banks of a small tributary 
on the left of the Anio not very far down. 
From Vicovaro onwards, then, all the four aqueducts remain on the 
left bank of the Anio. The deep valleys of some of its tributary streams 
create considerable difficulties for the aqueducts, and great bridges were 
required to cross them. Such is the aqueduct, nearly 200 metres long, 
by which the Aqua Claudia crosses the valley of the Fosso Maiuro. 
It was originally built partly in concrete faced with opus reticulatum 
and partly in ashlar masonry, resting on concrete foundations. The whole 
of the central portion of the bridge was strengthened at a later period. 
The brick facing of the reinforcing walls is fine work of the period of 
Septimius Severus. It is split by the roots of trees in several places, and, 
like other remains of the aqueducts, requires attention if it is not to 
collapse. The Anio Novus ran rather higher up, and avoided the 
difficulties into which the Aqua Claudia rather unnecessarily came, so that 
its channel is almost entirely underground, while the Marcia has a smaller 
bridge, of the time of Hadrian, lower down. Another example, also 
belonging to the Aqua Claudia, is the bridge over the next lateral valley, 
the Fosso della Noce; the greater part of it is of homogeneous con- 
struction, attributable to Septimius Severus, and is therefore a restoration. 
The central portion has collapsed, while on the further bank are traces 
of constructions and reinforcements of earlier periods. 
Two miles further down, the Aqua Claudia and the Anio Novus leave 
the river valley, and reappear in a small valley leading southward to the 
Valle d’ Empiglione, which is traversed by the road from Tivoli to Ciciliano 
and Genazzano. In this valley we find only one channel (where we 
should expect to find two), of rough concrete, belonging to the original 
construction, and measuring 1:20 metre wide and 2°60 or 2°70 metres 
in height—characteristic dimensions of the channel of the Anio Novus 
when running alone. It runs along the side of the valley, so that only 
one external wall is exposed, and this has later facing. The same 
difficulty presents itself when we reach the main Valle d’ Empiglione, 
for whereas previous observers have supposed that the two aqueducts 
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