Sunday 4 June 2023

Roman Aqueducts: Locating the Second ‘Chiocciola’ of the Aqua Virgo in Rome

In Evidenza

A spiral staircase of the Aqua Virgo lies completely obscured beneath Villa Borghese and the busy “Muro Torto” road and looks very similar to the famous Pozzo San Patrizio in Orvieto.

Deep under the Pincian hill in central Rome lies a spiral stairway that nobody ever climbs.   Just a few metres below the capital’s most popular park and one of its busiest roads, the stair descends into a pitch black tunnel, completely devoid of light.   But at the bottom of that helical stairway, there is no shortage of movement.   At the foot of the ramp runs pure, cold spring water, where it has flowed for 2040 years.

Today we can reveal that the precise position above the ground might have been located by well-known Roman speleologist Marco Placidi.   “I’ve identified the precise point with an Arva”[1] he told us, referring to the Arva brand of mountaineer’s radio-locator beacon.


But is Placidi correct ?

The Aqua Virgo is one of the most exciting aqueducts which have survived from ancient Rome.  It was completed in 19 B.C. by Augustus’ son-in-law, M.V. Agrippa, and parts of it, which are now dry and still show uniform Roman masonry can be visited like the stretch in the basement of the capital’s ‘Rinascente’ department store[2].   But the major part of the Aqua Virgo was restored in the sixteenth century by architect Giacomo della Porta and still flows right into the centre of the city where it supplies many of Rome’s most beautiful fountains.   This restored section is often known by Romans as the Acqua Vergine (the word for water is spelt in Italian with an extra ‘c’).

Whilst the parts of the aqueduct which have fallen into disuse show very clear signs of ancient masonry with magnificent arches and ancient brickwork, the part which still flows has had much of its masonry rebuilt and isn’t so recognisably Roman.   Archaeologists and maintenance engineers enter through a spiral staircase attached to the renaissance mansion Villa Medici, near the top of the Spanish steps and descend 25 metres to the level of Piazza di Spagna where, if they are wearing waders they can jump into the cold, flowing spring water.

I first walked through the water of the Aqua Virgo with Rome’s speleologist, Marco Placidi.   To get into the aqueduct we descended the first, well known spiral staircase known as the “Snail of the Pincian” (La Chiocciola del Pincio) and we wore chest-high rubber boots.   The first spiral staircase is well-known.  It is maintained by the water company Acea, and is the part of the aqueduct that film companies are taken to see.

Aqua-Virgo in Rome
The Aqua Virgo aqueduct in Rome- by Ted O’Neill

The Villa Medici chioccola was first built by Cardinal Giovanni Ricci da Montepulciano (1498 – 1574) who wanted to raise water from the aqueduct to supply his mansion above.   Ricci hired a famous engineer and swordfighter called Camillo Agrippa to install sophisticated water-raising equipment including water wheels and microscopic terracotta tubing embedded in the wall of the first spiral stairwell, the Chiocchiola del Pincio.

However the second spiral stairwell is much more interesting because it seems completely undocumented, because of its beauty and because it is only accessible from below inside the aqueduct.

This second stairwell takes almost an hour to reach, wading and pushing in the opposite direction from the heavy water 25m below the surface of the city.  The hard work of pushing upstream makes you lose your sense of time and position and in fact after a full hour you have only travelled between 550 and 750 yards.[4]

We have identified three possible locations above the ground for the second spiral stairwell based on the plan of 1964 and plotted these on a copy of the best map ever drawn of Rome, the 1748 Gran Pianta di Roma by G.B. Nolli.

The first point is two thirds of the way along the modern road called the ‘via del Muro Torto’ – the road of the twisty wall.   Here on the 1964 plan, is hand written ‘Chiocciola d’accesso’ – the snail of access.   That would seem to settle the matter, but we must remember that fewer electronic instruments were able to measure such things in the 1960s.

Aqua Virgo at the Muro Torto

Then on the same map, as the aqueduct passes close to the twisty-wall itself, the map labels a ‘Chiusino d’accesso ex-manufatto’ – manhole of access from the artifact /monument. Further on, beyond the wall, the plan labels a bipartite artifact/monument.   Any of these locations are possible, but recently, our collaborator, Speleologist Marco Placidi has made an astounding assertation. Placidi claims to have found the location of the second spiral stairway above ground.

Aqua Virgo

When we interviewed him for this article, Placidi was almost evangelical[2] about his discovery:

“At the bend of the ‘muro torto’ twisted city wall was an ancient cemetery known as the ‘Cemetery of the Impenitent’. Close to this cemetery there was a second spiral stairwell similar to the famous ‘Pincian Spiral’ but absolutely unknown.”

“It’s impossible to descend from the original entrance because the road passes there. A modern entrance has been made to descend into the aqueduct, but it can be found 30m within Villa Borghese [park – immediately to the East]. Now at the position of the original access there is only a flowerbed.” he said.

“To identify with certainty the exact point where the spiral came to the surface, we went into the aqueduct and we positioned an Arva radio beacon. This is a transmitter of vertically polarised waves and off-piste skiers use them to communicate their location if they become submerged by an avalanche. It’s an extraordinary instrument.”

It is unclear who is more accurate, Placidi, or the Acea map from 1964.   We would like to see some engineering documents from Comune di Roma from the building of the new carriageway of via del muro torto, which must surely reveal the truth.   And we would very much like to see this historical stairwell from the top in all its glory.

One thing is certain: Rome is still full of spectacular secrets.



[1] “Il punto preciso l’ho individuato con l’Arva” Placidi, M. (telephone conversation with O’Neill E. J. 17/01/2021)

[2] Pracchia, S., Pultrone, M., Saviane, N. 2017 “Acquedotti”. In Roma Rinascente: La città antica tra Quirinale e Pincio. Ed. Baumgartner, M. (De Luca).

[3] Andres, G. M. 1976 The Villa Medici in Rome (Garland) (68-118)

[4] 500-675m (Measurements: Google Earth)

[5] “Alla curva del muro torto c’era un antico cimitero, conosciuto come ‘Il cimitero degli impenitenti’. Vicino a questo cimitero, c’era una seconda chiocciola simile alla famosa ‘chiocciola del Pincio’, ma assolutamente sconosciuta.
Non si può più scendere dall’ingresso originale perché ora ci passa la strada. E’ stato fatto un ingresso moderno per scendere dentro l’acquedotto, ma si trova spostato di circa 30 metri all’interno di villa Borghese. Ora al posto dell’accesso originale, c’è soltanto un’aiuola.
Per individuare con certezza il punto esatto dove la chiocciola usciva in superficie, siamo entrati nell’acquedotto e abbiamo posizionato un Arva. Si tratta di un trasmettitore ad onde verticali e lo usano i sciatori che fanno i fuori pista, per essere ritrovati nel caso vengono sommersi da una valanga. E’ uno strumento straordinario.” (email conversation with O’Neill E. J. 24/01/2021)

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