Ubi's site about Rome, the Eternal City

The construction of the Aqueduct "Claudio" (of Claudius) was started by the well-known (not for his merits!) emperor Caligola in 38 A.D. and was finished by Claudio in 52 (but it was already active in 47); it was the eighth of the lines taking water to Rome.
It is considered the most important aqueduct of Ancient Rome and Claudio, who gave its name to it, spent immense resources for its accomplishment; the cost of techniques used and the increase of manpower were noteworthy for the time.
Pliny the Elder ("Plinio il Vecchio", in Italian, or "Gaius Plinius Secundus" in Latin, author of the encyclopedic Naturalis Historia) said that the total cost of the construction, together with that of the aqueduct of Anio Novus, costed 350 million sestertia (the Roman coin), equivalent to approximately 230 million of euro.
The main sources are called "Cerulea" (by its transparent blue colour) and "Curzia" (Fons Caeruleus and Fons Curtius), these could supply valuable water second in quality only to the Acqueduct Marcio water.
The sources were in the valley of river Aniene and generated two lakes near Monte di Ripoli ("mount Ripoli"), which is at the 38th (the Roman number is XXXVII) mile of via Sublacensis, between Marano Equo and Àrsoli. Today they can easily be identified with the source group of Serene sources (particularly the first and the second) and with the Saint Lucia lake.
It could also supply water from more sources and exchange it with the Marcio aqueduct but only part of it arrived in Rome: there were some legal intermediate provision points along the route and -history repeats itself- some illegal ones.

a well-preserved part of the Claudio aqueduct

The course of Claudio aqueduct was about 45 miles in the underground on the surface. The last part 4,5 km (3076 yd) was made out of bridges, in the upper part, while 10,5 (7095 yd) of arcades. The capacity was 4607 gallons (2211 liters) per second; what of it arrived in Rome went into the piscina limaria, together with the water of the Anio Novus.

The aqueduct starts following the right of the Aniene valley, maintaining keeping its height and shortcutting the curves of the hills. It passes by San Cosimato (a derivation continues to the right), Vicovaro, Tivoli, passing over small rivers with bridges which in part are still well conserved or intact in its original structure, in tuff, or with the restorations of the period of Flavius, Adrian and Severio.
Relevant is the the bridge in the ditch of Noce before Castel Madama, in two levels of arcades, about 135 meters in length.
After turning a long curve of Monte Sant'Angelo in Arcese, it passes by Tivoli, then goes to the south by via Prenestina and passing the deep valley between San Gregorio and Gallicano, with a very high bridge and into the well of Acqua Raminga, Mola of San Gregorio, Caipoli and Collafri. Later it turns to the west going to via Latina and Colli Albani.
The Claudio aqueduct passes the valley with the bridge on Fosso (ditch) of Acqua Nera, with nine arcades, in which the central part consists of two orders (the lateritium is typical of the period of emperor Settimio Severo), and the bridge on Fosso of Biserano, with only one arcade. There are "viadotti" about 80 metres long on the Fosso of Pallavicina, near the lake of Monno, and more in the Fossi of Marmorelle, Casale Mattia, and Prata Porci.
It comes to the area currently named Capannelle, out on the surface, passing the big pool (piscina) lamaria on a structure of a solid wall in blocks of peperino, then after 9.5km (6491 yd), till Porta Maggiore, (opus arcuatum) progressively on higher arches, the famous arches that characterized the landscape of the south of Rome that has been painted so many times.
The arches (on which it runs together with the aqueduct of Anio Novus) are constructed with peperino and red tuff, with transversal key blocks.

a pictoresque view of the Claudio aqueduct

The columns measure 3.35 meters with a depth of 3.10 meters, separated by 5.5 meters.
By the Casale di Roma Vecchia, you can find the longest intact route -about 1.5km-; the height oscillates between 17 and 22mt. In the depression of the Quadraro zone, the arcade is sustained by noteworthy pillars.

During the whole imperial period, the Claudio aqueduct was continually maintained and restored, starting from the time of Vespasiano: in 71 d.C. it was reconstructed after been closed closed for ten years due to the damage.
We lack written documents and we don't have much information about its reconstructions (after that of Tito, in year 81A.D.); we can guess thanks to the various techniques that were overimposed to the opera quadrata in tuff and travertino with the sides in opera reticolata.
You will find the opera listata of the time of Flavius, a mix from the times of Traian and Adrian, opera laterizia from the period of Severus and vittata of the late empire, plus more changes form the medieval period.
In modern times, parts of it have been reused damaging the parts of the original sturcture; this is particularly evident in the arches from Tor Fiscale to Porta Furba, where the aqueduct is crossed by via Tusculana.
A peculiar part is by Tor Fiscale, with a 13th century tower more than thirty meters high, built on the top of the two aqueducts.