Underneath the narrow streets, churches, and palaces of the Italian city of Siena lies a sprawling network of underground aqueducts that supplied water to the Tuscan city for centuries, enabling it to flourish despite a chronic lack of nearby rivers and streams. Extending for roughly 25 kilometers, the so-called Bottini constitute an ingenious hydraulic system that sustained the city from the Middle Ages until the early 20th century.
Fountain Fontebranda, its waters fed by Bottini. Credit: Wikimedia Commons
Siena is located in the central part of Tuscany, in the middle of a vast hilly landscape at an altitude of 322 meters (1,056 ft) above sea level. Although the elevated location provided defensive advantages, it created a major problem for the city's inhabitants. Unlike many Italian towns, Siena lacked a significant river flowing through its center. Securing a reliable water supply was therefore essential for survival and growth.
To solve this problem, the Sienese developed a unique underground aqueduct system. The first underground watercourses were already in existence in the 4th century, during the Roman period, but they were limited to the area of Castelvecchio. As Siena expanded starting from the 11th century, the need for a larger water distribution system was felt.
Construction of new aqueducts began during the 13th century and continued over the following centuries as the city expanded. By the end of the 14th century, the network had reached much of its eventual extent.
The city of Siena. Credit: Wikimedia Commons
They were called Bottini, a name probably derived from the Latin word buctinus, first recorded in a document of 1226, and may refer to the barrel-shaped vaults that characterize many sections of the tunnels. The term also recalls the Italian word botte ("barrel"), an apt description of the curved roofs that support the passageways.
Unlike the grand Roman aqueducts that carried water across spectacular arches, the Bottini operated almost entirely underground. The tunnels were excavated through the soft tuffaceous rock beneath Siena and carefully graded so that water could flow solely by gravity.
Most of the galleries are surprisingly narrow, averaging about 50 to 90 cm in width and 1.5 to 2 meters in height. A person can walk through them, but only with some difficulty. Along the floor runs a small channel known as a gorello, through which water flowed toward the city's fountains and reservoirs.
Brick-laid water channel of the bottini. Credit: Wikimedia Commons
The system collected groundwater and rainwater filtering through the porous soil. In some areas, the tunnels intercepted natural springs, while elsewhere they gathered water seeping through the rock. The gentle gradient ensured a continuous flow toward Siena without the need for pumps or mechanical devices. Maintenance shafts connected the tunnels to the surface, allowing workers to inspect and repair the network. These vertical openings also provided ventilation and access for cleaning operations.
The construction of the Bottini was laborious and dangerous. The workers responsible for excavating the tunnels were known as guerchi. Armed with little more than hand tools, they spent years digging through rock in cramped, poorly lit conditions.
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Local folklore held that the guerchi occasionally encountered mysterious underground beings known as omiccioli and fuggisoli. The former were described as small goblin-like creatures, while the latter appeared as sudden flashes of light. Modern writers have suggested that these visions were probably the product of fear, exhaustion, darkness, and perhaps the wine that formed part of the workers' compensation. Whatever the truth behind the stories, the dangers were real. Tunnel collapses, poor air quality, and the constant challenge of maintaining accurate gradients made the project an extraordinary feat of medieval engineering.
The amount of water a household received was controlled by a small calibrated hole, called a dado or forellino, cut into a metal or stone plate placed across a diversion channel. Water passed through this hole at a predetermined rate. Credit: Wikimedia Commons
Credit: Wikimedia Commons
The Bottini supplied water to Siena's famous fountains, wells, and public washing places. Among these, the Fontebranda was the city's oldest and most celebrated fountain. Its abundant water supply supported households, laundries, animals, and local industries. Tanneries, dye works, and mills all depended on the steady flow delivered through the underground channels.
Another major branch supplied Fonte Gaia in Piazza del Campo, one of Siena's most iconic landmarks. The overflow from this fountain continued onward to feed smaller fountains elsewhere in the city.
For centuries, these fountains served as communal gathering places where residents collected drinking water, washed clothes, and conducted daily business. Without the Bottini, medieval Siena could never have supported its population or its thriving economy.
The Fonte Gaia fountain. Credit: Wikimedia Commons
The network eventually developed into a complex web of primary and secondary channels. Two main branches became particularly important. The oldest was the Bottino Maestro di Fontebranda, which carried water from the area of Fontebecci to the great fountain of Fontebranda. Built at considerable depth beneath the city, it formed one of the backbone arteries of Siena's water supply. The second major branch was the Bottino Maestro di Fonte Gaia, constructed around 1300. This channel fed the famous fountain in Piazza del Campo and several other fountains through overflow systems. Numerous smaller branches extended throughout the city, creating a remarkably comprehensive water-distribution network.
Beyond supplying water, the Bottini had military significance. Because the tunnels extended beyond the city walls, Sienese authorities feared they could provide a hidden route into the city. In 1467 several external entrances were closed for security reasons, and a conspiracy in 1526 allegedly involved plans to bring enemy troops into Siena through the aqueducts. During the siege of 1554, forces allied with Emperor Charles V reportedly attempted to exploit the Bottini, prompting defensive measures to block access while maintaining the water supply. Centuries later, in June 1944, Italian partisans considered using the tunnels to liberate German-occupied Siena but ultimately abandoned the plan.
Fontana dei Pispini, one of Siena's many fountains. Credit: Wikimedia Commons
For hundreds of years, the Bottini remained Siena's principal source of water. Only in the early 20th century did the city gain a modern aqueduct bringing water from the Vivo springs on Monte Amiata. With the arrival of piped water in homes, the medieval system gradually lost its central role. Yet the Bottini never disappeared. Much of the network survives in remarkably good condition, and parts of it continue to supply several historic fountains.
Today, guided tours occasionally allow visitors to descend beneath the city and walk through sections of the ancient passageways.
References:
# Bottini of Siena. Wikipedia
# Bottini in Siena. Ambito Terre di Siena
# The Bottini of Siena
# The Route of the Bottini
# The Underground Bottini of Siena. Labellezzadellacarta.it
# The ancient underground aqueducts. Visit Siena
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