Roman aqueducts - structure and functioning By Prof. Arch. Renata Bizzotto With the collaboration of Arch. Maria Letizia Mancuso The aqueducts collected water from several natural springs located a considerable distance from the city (the furthest was that of the Anio Novus , 59 miles or 87 km east of ).

The springs in Rome The "water" was chosen as a consequence of many factors: its purity, its taste, its temperature, its supposed medicinal properties, attributed to the contained mineral salts, and the position of its sources, which had to be visibly pure and limpid, inaccessible to pollution and free of moss and reeds. The general conditions of the beasts that consumed them had to be examined. If the source was new, the samples had to be analyzed in good quality bronze containers to ascertain the corrosion, effervescence, viscosity, foreign bodies and boiling points. The water moved in the direction of the city thanks to no other force except that of gravity, ie the acted as a continuous slide for the whole distance that separated the springs from the point of its outlet. To obtain this result, each of them was designed in such a way that every single part of the long track corrected slightly lower than the previous one, and slightly higher than the next one, so as to obtain an average slope calculated around 2%. For this reason, the water had to be taken from sources located in the hills, higher than the position of the Roma, particularly in the area east of the city, and every step of the long journey had to be carefully planned, depending on the characteristics of the soil that he met.

Diagram of a chorobates

Diagram of a dioptra The Roman architects were skilled in this activity, for which they had sophisticated tools: apart from the common water level (pound), similar to that used today by carpenters, they used tools such as chorobates , and dioptra . Before being channeled, the water passed through one or more pools called the pool limariae , where the flow velocity slowed down, allowing the mud and other particles to settle. Similar tanks were also found along the course of many aqueducts, to remove any impurities.

Swimming limariae

Vertical wells Far from the urban area, most of the aqueduct route was underground: digging vertical wells the height required to maintain a downward path was reached, and then the canal, or specus , was dug through the rock.

The specus

The remains of the aqua specus Alexandrina Because of the characteristics of the terrain, some parts of the duct had to run on the surface, along a ditch whose walls were reinforced with a palisade. Along the external route of the aqueduct every 240 feet (71.28 m) a large stone, called a cippus , signaled the presence of the underground channel, and to avoid damage and pollution a safety distance of 15 feet (1 Roman foot) had to be respected = 29.7 cm) for each side of the structure outside the city and 5 feet in the case of an underground structure or structure within the city.

Diagram of the stone

Diagram of the bridge In fact all the aqueducts were public, owned by the government for the benefit of citizens, despite the ius did not provide for expropriation (it is thought that the forced suicide of Torquato in 64 AD and the seizure of its estates is to be charged to the construction of the Arcus Neroniani ). Their damage or pollution was severely punished, as well as using water for villas or private land by illegally connecting to public pipelines. Private branches did indeed exist, but they could only use the surplus of available water, and to do this they paid a tribute. When the duct reached a steep wall or a gorge, a possible solution was to build a bridge , or viaduct, to cross the jump and reach the opposite side at a slightly lower height: here the path of the canal returned underground.

The inverted siphon

Diagram of the arches A 'no other way to overcome these natural features could be crossed with the "inverted siphon", a technique based on a simple physical principle. Where the ground was level, near the city, the flow was made possible by building the famous series of arches , some of which reached almost 30 m in height.

Arches

Arches

Arches

Arches They crossed the countryside for miles, keeping the water level high enough to reach the urban area. In fact it was along these grandiose structures that most of the aqueducts entered Rome. More traveling the high water, the greater was the number of neighborhoods that could have achieved. In the upper part of these viaducts, where the canal ran, there were openings that allowed the same maintenance work required by the underground ducts.

The three "waters" - Multiple conduits above and Having to exploit as much as possible the natural height of the territory crossed, several aqueducts arrived in Rome following an almost identical path; then two or even three "waters" could share the same viaduct, flowing in separate canals at different levels, according to the respective height that each of them had reached so far. The main citizens outlets were located in the highest urban points. In particular, many aqueducts reached the borders of Rome from the south-east, in a site called Spes Vetus ("old hope") from an ancient Temple of Hope that once stood there. The water then entered the city from the nearby Esquilino hill, from where it could be distributed to most of the other districts. In some cases, more "rich" aqueducts helped others to maintain a volume of water sufficient to supply the respective areas: for example, the Aqua Claudia poured about 1/8 of its capacity in the A.Iulia and A.Tepula . Not all the aqueducts entered Rome via a viaduct: the oldest one, the , ran almost completely underground, as well as those coming from the north-west, Aqua Alsietina and , which supplied the VIII regio, Trans Tiberim (ie Trastevere) from the top of the Gianicolo hill. In these cases, the lapides were used within the urban area perterebrates : special hollow bricks that fit one into another forming an impermeable conduit. lapides perterebrati

The castellum The main outlet of an aqueduct had the appearance of the castellum ("castle"), a structure of variable dimensions that contained one or more pools similar to the swimming pool limariae , where the water flow slowed down and the last impurities sedimented. The water was then poured outside by a certain number of goblet-shaped fillets. Educational proposals

The author

Prof. Arch. Renata Bizzotto