The Aqua Alexandrina was the last aqueduct built in ancient Rome. It was built in 226, 500 years after the first one. Its purpose, according to the Emperor Alexander Severus, who paid for the construction, was to deliver water to the Thermae of Nero, located in the western part of the Field of Mars, approximately on the site of today’s Piazza Sant’Eustacho (St. Eustathius Square).
The new aqueduct collected water from springs located about a mile south of the via Prenestina, east of Rome. The original direction of the aqueduct was parallel to the road, and then veered slightly south to the via Labicana (present-day via Casilina).
Approaching the city walls, it turned into an underground canal and entered the city, probably through the Porta Prenestina (present-day Porta Maggiore), from where it went to the Esquiline Hill and then to the Quirinal Hill, descending from the latter to the plain of the Champ de Mars.
There are still standing parts of this aqueduct, up to its intersection with the Via Casilina in the Torpigniattara area. The rest of its route remains hypothetical, as the Aqua Claudia with the Anio Novus, the triple canal Aqua Martia, Tepula and Julia, as well as the Anio Vetus, passing, however, below ground level, stood nearby. The underground channel Aqua Alexandrina was never discovered.
The longest parts of the aqueduct within the urban area can be seen on the eastern outskirts of Rome. However, outside the city it has a fairly good preservation for most of its length.
The first surviving section is located on the viale del Aquedotto Alessandrino, where a continuous chain of arches crosses 250 meters of public garden.
On the Via Casilina, near the southeastern end of this section of the aqueduct, one can see an interesting but not too well known ancient structure – the monumental tomb (mausoleum) of St. Helena, mother of Emperor Constantine the Great, who died in 328. It is a round brick hall that had (but long ago destroyed) a high dome and stood at the entrance to the Christian catacombs of St. Marcellinus and St. Peter.
Around the hall are eight niches. One of them corresponds to the entrance, and in the niche opposite stood a large sarcophagus of red porphyry, in which the body of St. Helena rested. This sarcophagus is now preserved in the Vatican Museums. The central space of the structure is now occupied by the tiny church of Santi Marcellino e Pietro, built in the early 17th century.
Following late imperial methodology, the weight of the dome was reduced by inserting empty clay pots into the building material. This gave the burial ground the folk name Tor Pignattara (Pot Tower), which later became the name of the entire neighborhood.
The other surviving section of Aqua Alexandrina is located about one kilometer to the east, at the southern end of the densely populated Centocelle district. It is of comparable length to the first and has a very well-preserved exterior brick structure. Fortunately, a major highway crossing the central part of this section of the aqueduct does not affect its condition in any way.
The new construction techniques developed over the previous century meant that the Aqua Alexandrina was not lined with large blocks of tuff, but with a layer of bricks. Its internal structure remained traditional. A distinctive feature of the aqueduct are four small white travertine brackets protruding over each pillar, just below the arch. Their purpose is not clear.
In the area of Centocelle, the Aqua Alexandrina reaches its maximum height of more than 20 meters above ground level. In fact, the aqueduct crossed a large ditch in this place, as the sloping streets still tell us.
If one examines the aqueduct in both directions from this place, i.e. along the Via del Pioppi towards the city and along the Via degli Olmi towards the suburbs, one can note its gradual decline in relation to the ground level.
The part towards the town ends with the complete disappearance of the pillars and the possibility to see the tunnel structure at ground level.
PICTURE ON THE LEFT At the place where the section of the aqueduct that runs along the Via degli Olmi ends, there are the ruins of a medieval watchtower. It is believed that the presence of such a tower signifies the functioning of the aqueduct in the early Middle Ages. This would justify the construction of a defensive structure near the aqueduct.
The last traces of the Aqua Alexandrina in the city limits can be seen by walking further along the via degli Olmi for about 200 meters. Here the roads go downhill again, and a large fragment of two arches indicates that the aqueduct crossed another ditch.
Another preserved section of the Aqua Alexandrina, about 150 meters long, crosses the public park of Tor Tre Teste. Here its height reaches 4 meters, which is very low compared to the previous section. The brick cladding is almost completely lost, but the overall structure is better preserved than in the Torpigniattara area.
The aqueduct then becomes so low again that its tunnel is at ground level, after which it disappears completely.
It is worthwhile to finish the aqueduct survey here, although there are two more fragments of the Aqua Alexandrina in a field about 350 meters further east, which can be seen from the road surrounding the private area, but cannot be approached.
