The Route of the Bottini

There are two principal branches of the bottini, situated at two different depths: the main bottino of Fontebranda, that brings water from Fontebecci and the branch of Chiarenna (in the zone north of Siena) to Fontebranda and runs quite deep, and the newer but longer main bottino of Fonte Gaia, which also fills other fountains at lower elevations (Casato, Pantaneto, S. Maurizio, S. Giusto) with the overflow of Fonte Gaia.

The main branch of the Fonte Gaia continues toward its sources until Fontebecci where it divides into two branches, one that originates at Colombaio and the other at Uopini and at San Dalmazio.

In order to make water arrive at the Piazza del Campo, at an elevation of 320 meters above sea level, it was necessary to search for a source at an even higher elevation, therefore to the north, along the ridge that from extends from Porta Camollia and arrives at Fontebecci and beyond, the only direction that is not interrupted by the deep valleys that occur in the east, west, and south of Siena. And from the north, in open country, the two main bottini collect great quantities of water that filter from the fields overhead, this factor however requires the tunnels to be faced with brick in order to keep the water-soaked limestone from collapsing and obstructing the channel through which the water flows.

This brick facing is often absent from those parts of the bottini which run under the city because the buildings and paved streets prevent the infiltration of water, and thus the limestone remains dry, reducing the risk of cave-ins. Precisely to prevent dangers of this sort as well as other damage caused by the carelessness of owners of the land above the bottini, or adjacent to the ventilation shafts, the city enacted a series of very severe laws that prohibited foreigners from entering the tunnels; or cultivation or the manuring of the strip of land above the route of the tunnels (in order to avoid the growth of roots that would ruin the tunnels and dirty the water); or the taking of water for private use by the bottino's abutters; etc. Above all, the fear that anyone who entered the tunnels could quietly navigate under the city brought about the decision in 1467 to close various entrances outside the city walls. It was not accidental that various enemies attempted to penetrate the city's defenses through its aqueducts: the most famous case was that of 1526 when Pope Clement VII promoted a plot to overthrow the Sienese government and found an ally in Lucio Aringhieri, who promised to have his troops secretly enter Siena through its aqueducts. The plot failed because a carpenter, of whom the plotters had requested some stairs, grew suspicious and warned the authorities. Also, during the siege of 1553 the bottini were barred in the hope that the water supply not be interrupted.