Subterranean Siena

A walk beneath Siena to explore its medieval waterworks

In a hilltop town which lacks a natural spring, where does the water in that fountain come from?

Walking around Siena one happens on a variety of medieval wells. Yet Siena is not naturally rich in water: it is a hilltop settlement and situated far from the great rivers of Tuscany. Until World War I the city relied on a water supply system constructed in the Middle Ages: 25 kilometres of channels and side-channels, an underground aqueduct winding under the entire city. They are called the bottini, a name perhaps related to the barrel shape of the passages, botte being barrel.

 

There are various branches of this system on two levels: the Fontebranda is very deep while the Gaia is several metres below street level.
Just off the via Camollia in a lane framed, this time of year, by wisteria, stands an ancient brick wall. Above a small iron door in this wall a plaque announces:

FONTE GAIA

ingresso di Fontegiusta

(GAIA FOUNTAIN

Fontegiusta entrance)

Fonte Gaia has been Siena's pride - and saviour - since 1343 (after 9 years of digging) when complex excavation and construction brought water to the city from springs in the Tuscan hills 25 kilometres away. The name Gaia (joyful) is supposed to derive from the joy of the citizens when running water finally flowed in Siena's main square. How the water reached the hilltop city is a fascinating story narrated via a 90 minute tour of the city's underground tunnels.

The Fontegiusta well is situated just off what was once the via Francigena, the major pilgrim route to Rome; water was something all pilgrims were entitled to along their way, but Siena in any case was in dire need of a constant and reliable water supply, having no springs, aquifers or rivers of its own. By the 14th century the city's population had increased exponentially; indeed it was the same then as it is today, around 60,000.

One sees only a fraction of the tunnels as the tour travels just over a kilometre. Not advised for the claustrophobic, it requires some navigation of steps, some puddles and slippery bits and straddling water channels, plus you must watch out for your head and for a very short stretch doubling over is necessary. A torch is essential, plus sensible, waterproof footwear.

the lowest part of the tunnel: since it is shored up with bricking presumably there were some structural problems here

Calcium deposits, small stalactites and tiny filaments of plant roots  tipped with droplets of water which glint like crystals, line the damper areas of the tunnel. 

calcium deposits and at right, water droplets hang from root filaments on the ceiling

Although the engineering feat of this ancient hydraulic enterprise is most impressive (more on this below), I was deeply struck by the sheer hard work involved in creating 25 kilometres of tunnels, alcoves, water channels, decantation areas, side-channels, wells and spy-holes. 

Imagine an army of Maremman miners (Siena worked mineral mines along the coast and brought in the miners and their families to create the waterways) labouring in shifts night and day by the light of candles, chipping and hewing their way through layers of hard sandstone.

The sandstone is so hard it has largely not crumbled or caved in over 650 years, and no labourers are documented as perishing in the excavations (frankly I find this incredible, but there you are). Some sections are geologically revealing: sandstone layers alternate with pebbled layers, which were pushed upwards by earthquakes  10 to 30 million years ago during the Pleistocene, denoting various periods of violent earthquake activity millions of years apart.

alternating layers of sandstone and rounded pebbles, our clue to geological movements over the ages

Imagine excavating all this with iron picks. The tunnel surface is pocked with pick-axe marks whose angles reveal the direction in which the work was moving.Different teams would work from opposite directions to meet in the middle; sometimes miscalculations were made which explains the occasional variations in the tunnels' width or height. Innumerable documents survive to recount the facts and figures of this enormous undertaking.

occhio/miraglio (the latter originating from the Spanish mirar, to see, interestingly, because the workers came from the coast and contact with Spanish traders)  or spy-hole shaft, hewn by masters

At regular intervals huge shafts were carved into the tunnels to serve as spy-holes (called occhi, eyes, or miragli) for regulating the direction the tunnel was taking. They also let in air for the workers, while debris was hauled up and out using pulleys and the workers' meals were lowered down, to save time. And of course the diggers and their teams would enter and exit from these openings. The sides of each shaft opening are deeply grooved by the pulley ropes.

symbols like this appear at the entrance to side-channels and alcoves. It is thought that they are rudimentary numbers, possibly of Arabic origin. In other areas small ogival niches can be seen, roughly crosshatched or decorated. Apparently these once housed little images of the Madonna. The miners were said to be highly superstitious (unsurprisingly, given the period and the nature of their work). Tales were told of mischievous underground sprites and will-o'-the-wisps (fuochi fatui)

The miners worked in shifts and their labour was strictly hierarchical, according to the trades' practice of the day. There were the head excavators, the workers, and the rubble-clearers. The last were made up of women and children, probably the 'immigrant' miners' family members. The tunnel workers were called guerchi, a corruption of ciechi or 'blind ones', because when they emerged from the candlelit tunnels they were as if blinded.

One of the channels, called gorelli: along the sides the calcified accretion is visible; every decade or so this has to be removed; niches along the tunnels are stacked with these limestone shards. The only sign of life in the tunnels are the algae clinging to the sides of the channels.

tiny shell fossils and imprints of shells proving that all this was a seabed in prehistoric times

The most impressive aspect of the entire feat from the point of view of the engineering is how the grading of the channels' angle was gauged, from the 25 kilometre-distant source in the hills all the way to the wells themselves. The whole system relies on gravity to bring the water to Siena, yet apparently the gradient lowers only one metre every kilometre which is very little; this slow water flow allowed the calcium and other impurities to settle to the bottom. 

Technically, this fine gauging of the gradient was achieved through a simple device, used by Ancient Roman, Greek and Egyptian  engineers: the archipendolo - for which I have been unable to find a satisfactory translation. The device contains a plumb line but in addition allows for measurement of the angle. It is cross between a plumb line and a level.

archipendolo - plumb rule, the closest translation I can find but hardly descriptive or accurate

To compensate for error and unavoidable alterations in this gradient, towards the lower end of the slope the channel was angled in deliberate switchback detours to further slow the flow of the water. Admittedly it is an imperfect system: in this area we encountered puddles.

deliberate switchback to slow down water flow

The city of Siena drew on this water supply from the many public wells dotted about the city, the Fonte Gaia in Piazza del Campo being only the grandest and most celebratory - and perhaps one of the last in the sequence, since it is located in a low area of the city. 

Over time private citizens and institutions asked to be connected to this bounty. Private wells and secondary channels were dug: but how to charge for this privilege? A simple method was devised by which individuals could subscribe for dadi (a word meaning 'nut' as in nuts and bolts) which corresponded to the amount of water flow as it emerged from the standard hole. The minimum assessment was 1/3 of a dado, the maximum 3 dadi. Since there was no way of regulating the flow, this estimate was based on optimal results; if there were a drought the assessment was the same, regardless of supply. In the second half of the 19th century painted plaques next to these individual water channels described the families or institutions involved, including their address and the amount for which they subscribed. Note below that the Capuchin nuns were exempt, the Church enjoying fringe benefits, then as now. On the other hand, anyone caught stealing water from the bottini was summarily arrested.

campaign slogan from late 19th century

each plaque includes a map of the wells and corresponding streets; this one contains a little partisan campaigning: the crest is that of Siena and below is written Viva Il Sindaco,(Benedetto Tolomei, whose descendants live in Siena to this day) Long Live the Mayor.

free water for the Capuchin nuns

Here many families, many of whose descendants populate Siena today, joined the bandwagon, mostly with a single dado

At the end of this tunnel the bottino widens out into a decanting area where the calcium/lime content and other impurities of the water was allowed to precipitate.

decanting basin

As we exit the bottini open out into a cavernous hall alongside which the decanted water rushes like a waterfall down small steps, as if hurrying to meet the outside world and its destination, the Fonte Gaia.

water finally gushing down a man-made cascade on its way to the Fonte Gaia

our guide Antonio showing us the map of the various bottini

In a way it felt as though we ought to have started the tour here: hard hats hung on the wall - it might not have been such a bad idea to wear one; a map illustrated the entire network of tunnels and there was the space and atmosphere for the perfect introductory talk. On the other hand it was more logical and exciting to follow the flow of the water than go against it, and once we exited, there was Piazza del Campo before us, in all its glory. 

the endpoint of the walk, which might also be the starting point, is this trap or large manhole which opens onto a bar/caffe' on Piazza del Campo!

detail from the Fonte Gaia: the she-wolf mother of Romulus and Remus, one of the symbols of Siena and part of its claim to an ancient Roman heritage

The handsome white marble fountain which has reigned in Piazza del Campo since 1419, was sculpted by Jacopo della Quercia but restored and altered somewhat in the 19th century. The damaged original sculptures are on view at the museum of Santa Maria della Scala, opposite the Duomo.

There is also a Museum of Water, il Museo dell'Acqua, in Siena: I hope to be able to post on that too, in the future.

The bottini can only be visited in spring and autumn when the water level is low. Booking is way in advance, 

over a year in our case. 

Requests must be made in writing to the Comune of Siena - Servizi Idrici -Via di Citta', 81, 53100 Siena.

The volunteer guides are organized by La Diana Siena
(The association's name derives from a legend originating during the excavation of the bottini: workers swore they could hear a river rushing in the earth below them, but it was never found and in fact does not exist. This phantom river was named Diana.)

Tickets cost 9,30 euros and cover insurance for visitors. 
The tour in Italian is included in the price.
Remember:
 gum boots/ wellingtons if the water level is high, 
but specially, a torch. 

For a very informative and detailed site which elaborates on much of the above, have a look here.