Aqua Alsietina

The Humblest of Roman Aqueducts

On 4 March 2011 my wife and I were privileged to form part of a small group led by the now-famous Aqueduct Hunters, Mike and Ted O’Neill, to visit the southern shore of Lake Martignano and explore the intake of the ancient Roman aqueduct, Aqua Alsietina. Lake Martignano lies in a small volcanic crater close to Lake Bracciano some 27km North-West of Rome. It was a cold and gloomy day and hardly anybody else was to be seen in this popular recreational area.

Mike O’Neill, Ted O’Neill, Ira Levin (behind), Loretta Cole, Ted Cole
Photo © E. Cole 2011

The Aqua Alsietina is the least well-known of the 11 Aqueducts of Ancient Rome. It was also the lowest of them all; travelling underground for most of its length and leaving no eye-catching arches or sub-structures to draw attention to itself. Its existence would probably not be known today if it were not for a book written around 100AD by the then Water Commissioner of Rome, Sextus Julius Frontinus, in which he described the nine aqueducts existing in his day.

Frontinus¹ tells us that the Emperor Augustus built the Alsietina in 2BC to provide water for his Naumachia, an artificial lake to the South-West of Rome (now Trastevere), on which naval triremes could stage mock battles. Its length was 33 km, almost entirely underground. The quality of the water was not an important consideration for the Naumachia; what did matter was quantity.  Lake Martignano, then known as Lake Alsietinus, was chosen as the source, probably because of its proximity to Rome, its high elevation (207 metres above sea level) and the possibility of cutting a reasonably straight route for the aqueduct channel.

Frontinus states that the Alsietina had no catchment basin at its intake and that its water was augmented by a branch supply from neighbouring Lake Bracciano, the waters coming together at a place called Careiae which is unknown today. According to him the quality of the water was foul, fit only for filling the Naumachia and for irrigating gardens.

Today, the only visible remnants of the Alsietina are its intake at Lake Martignano and a very small section of its channel in Trastevere, close to Piazza S Cosimato. This made our visit all the more interesting. The intake is cut into the crater’s sloping wall some 12 metres above and a long way back from the current water of the lake. The opening is about eight feet high by three feet wide and leads to a smaller tunnel heading in a southerly direction. The walls of the opening and of the tunnel are severely eroded and no trace of Roman brickwork remains. Just inside the entrance there is a large hole in the floor, about two metres deep, which makes access to the channel beyond very difficult without a plank or a ladder.

The intake or incile of the Aqua Alsietina at Lake Martignano
Photo © E. Cole 2011

It has to be said that the remains of the intake are not particularly impressive. Viewed from the outside they could easily be mistaken for a natural cave. They do, however, prompt some interesting thoughts and observations which I will explore briefly.

First, its identification. There is little doubt that Lake Martignano is the ancient Lake Alsietinus which supplied water for the aqueduct. It fits the location given by Frontinus and the intake we visited is exactly where we would expect to find it on the South-East slope of the crater wall. But leading aqueduct scholars of the late 19^th and early 20^th century were less certain. Thomas Ashby³ observed in his seminal book The Aqueducts of Ancient Rome, published in 1935, that the shore at the South end of Lake Martignano was flat, an impossible siting for an aqueduct intake. His observation was correct, as far as it went, but he did not allow for the possibility that the water level may have dropped significantly since 2BC. He went on to say that the Southern slope of the crater wall was in his day covered with dense undergrowth making it impossible for anyone to see an opening that may (or may not) have existed up there.  As an aqueduct hunter I can sympathise with him.  Today the undergrowth is less dense but in fairness to Ashby the intake is not easy to spot. When you climb the steep South-Eastern slope you come upon it almost by chance. It is partially hidden in a cavity, suggesting that it may have lain buried for a long period and then been brought back to view by excavation. If this is so, the timing of the excavation must have been more than 30 years ago as photographs of the intake were published in at least two books⁴ in the early 1980s.

Next Vitruvius: "...clay in wicker baskets made of swamp rushes
should be packed-in amongst the props..."

« 1 | 2 »

1. Sextus Julius Frontinus, “The Aqueducts of Rome” published in 1980 as part of the Loeb Classical Library by William Heinemann, pages 252, 361, 363 and 365.

2. Extract from map included with “Thomas Ashby, Un Archeologico Fotografa La Campagna Romana Tra ‘800 e ‘900”, published in 1986 by The British School at Rome.

3. Thomas Ashby, “The Aqueducts of Ancient Rome” Published by Clarendon Press, OUP 1935, Chapter VII.

4. 1. “Il Trionfo Dell’Acqua, Acque e Acquedotti a Roma”, published in 1986.by Museo della Civilta Romana, Roma. Page 73.
   2. Pietrantonio Pace, “Gli Acquedotti Di Roma”, published in 1983 by Art Studio S Eligio. Page 148