Construction performances and management of ancient aqueducts
Among the problems to be faced in designing an aqueduct, the choice of spring is the most important. Important factors that determine selection include water quality, quantity and regularity of flow. A key factor is the altitude of the point of water collection in respect to the terminal, in order to ensure the right slope of the entire course and consequently a constant flow smooth and not too impetuous.
An aqueduct generally began with a collecting basin for surface water; in case of groundwater wells and tunnels, the dug (caput aquae) dammed the veins in a single duct. Then a settling tank (piscinae limariae) allowed the first impurities deposit. From here the water was fed into a channel (specus) which permitted to maintain a gentle slope. To do this, in some cases, it was decided to lengthen the path of the track, in order to accommodate the natural features of the land and maintain, as much as possible, a smooth slope. For this reason, many roman water systems are longer than the linear distance between the source and the point of delivery.
Generally the course was underground, in perticular dug into the rock, in some cases it ran close to the surface, covered with stone slabs or signaled by cippi along the way (ingeriali); when the duct crossed rivers or depressions, it run up walls or arches. At the end of the course there was a building (castellum aquae) from which water was distributed in urban pipes for users. The flow of an aqueduct, in ancient Rome, was measured in “quinary” (1 quinary corresponded to 0.48 l/s, that is 41.5 m3/d).
Until the imperial era, responsible for the care aquarum was the censor, the magistrate in charge for public works, usually with a “aedile curule”. The censor usually relied on the construction of an aqueduct through a concession contract, and then took care of the final test, while the aedile curule was charged of water distribution and dispensing.
After the year 12 BC the water management passed into the Emperor hands, who gave it to a team of three senators; one of the three, nominated at consular level, was appointed “curator aquarum”. The status of this officer allowed an absolute control of the urban water management. His numerous staff consisted of engineers, architects, technicians, administratives and 240 “public slaves” maintained by the State.
Sextus Julius Frontinus
Sextus Julius Frontinus was a vital water commissioner (curator aquarum) who lived in the 1st century AD. He was in charge of a staff of technicians and workers involved in the construction and maintenance of waterworks. He reformed the preceding water management system in order to correct the existing abuses and favouritisms. He also wrote “De aquis urbis Romae”, a cornerstone that is, inter alia, a precious reservoir of information concerning ancient Roman aqueducts (including information on the location, length, source site, scope, water flow, names of manufacturers, technical specifications, measurements and methods of construction and distribution). All our knowledge on the administration, management and regulations relevant to the ancient Roman aqueducts are derived from that treatise (in particular the lex Quinctia proposed by the consul Quinctius Crispino in 9 BC, which shows the Frontino full text).
Frontino didn’t mention the Trajan’s Aqueduct as he died in the year 100 AD, nine years before the opening of the aqueduct itself.
This was a large amphitheatre filled with water in which Roman people loved to reconstruct naval combats for entertainments. They were representations of historical naval battles really took place or invented.
Slaves, prisoners of war and sentenced to death would take place on the ship or swim in the water to make their performance during a battle. At that time, it was a very popular show with authentic warships. Emperor Augustus had made a very large Naumachia in the Trastevere area, with a capacity to accommodate up to 30 warships.
There are evidences that Naumachia was still in operation in the 3rd century AD, for which the Trajan’s aqueduct was still running, but afterwards it was abandoned due to a natural lowering of the lake Alsietinus, who left the duct dry.
Aqua Traiana celebration
In 109 AD Emperor Trajan had coined a special coin, a “Sestertium” to celebrate the completion of the aqueduct. On one side the coin figured the Emperor Trajan and on the back a semi-reclining figure representing a River God under a large arch dominating two columns.
For centuries it was believed that the image referred to a monumental fountain that the emperor aspired to build on the Janiculum; and this was eventually realised 1500 later, by Pope Paul V (Fontanone). According to O’Neill Brothers (British documentary makers) the large arch represented the cave-nymphaeum of Bracciano.
According to some historians the Sestertium coin has been distributed throughout the Empire aiming to celebrate the Trajan success and to underline that the aqueduct has been built at his own expenses.
Nymphaeum and Trajan Caput Aquae
Two British documentary makers, Ted and Michael O’Neill have discovered in 2010, the initial source of the aqueduct opened in 109 AD by Emperor Trajan: the Aqua Traiana. Such a finding has been possible thanks to a hint given in the book “The Aqueducts of Ancient Roma” published in 1935 by Thomas Ashby, (Director of the British School at Rome from 1906 to 1925). The Caput Aquaewas found near the stream “Fiora”, between the towns of Bracciano and Manziana and was included in a ancient cave-nymphaeum.
Almost certainly this is the same spring used from the aqueduct built by the Orsini family in 1575 and then rebuilt in 1727 by the family Odescalchi (Odescalchi aqueduct), following the same path, to feed the little Duchy of Bracciano that had few thousand of inhabitants.
This has been actually a “rediscovery”, as the cave and associated Roman hydraulic structures were known, but information about them were lost and/or considered of little interest. In fact, the cave and hydraulic works were wrongly attributed to a small local aqueduct used for the Forum Clodii: This is a Roman settlement situated on the slopes of the catchment area in the locality of Vigna Grande – between Bracciano and Trevignano, below Manziana).
In 1575 this cave-nymphaeum was converted into a chapel dedicated to the “Madonna del Fiore” (Madonna of Flower). The cave, plastered and painted, was in bad condition, while the building structures for hydraulic tunnels are reticulated brickwork and well executed (opus reticulatum).
Aqua Alsietina – Aqua Traiana confusion
The confusion is caused by the strange Latin inscription on the attic of the prestigious Janiculum fountain. The inscription recalls Aqua Alsietina and not Aqua Traiana.
The inscription writes:
PAULUS QUINTUS PONTIFEX MAXIMUS
AQUAM IN AGRO BRACCIANENSI
SALVEBERRIMIS E FONTIBUS COLLECTAM
VETERIBUS AQUAE ALSIETINAE DUCTIBUS RESTITVTIS
XXXV AB MILLIARIO DVXIT
When in 1610, Pope Paul V wanted to improve the water supply of the city, he gave order to restore the existing aqueduct coming from the mountains Sabatini. It is probable that the engineers were not aware of the Aqua Traiana, but only of Aqua Alsietina. This is possibly due to the fact that Frontinus, in his treatise “De aquae ductu urbis Romae“, referred to the very short life of Aqua Alsietina, but not to Aqua Traiana. (This was because he died 9 years before the aqueduct finished).
The “rediscovery” of the Aqua Traiana happened in 1680 thanks to Raffaele Fabretti, who used ancient sources of information available by the Paul V chancery. This mistake probably, would have been avoided if more researches were available than the work of Frontinus. It is unlikely that the water engineers and managers of renaissance and baroque period would ignore such references. Such a reconstruction of events allows us to explain the mistake that a visitor can find on the above mentioned Latin inscription.