There is a mountain in Piedmont that has been supplying Milan without charging a fee since October 24, 1387. On that day, Gian Galeazzo Visconti granted the Veneranda Fabbrica the right to use the Candoglia quarry, with free transport of the stone blocks all the way to the city.
Ever since then, every spire, every ornament, and every statue that needs replacing—among the Cathedral’s 3,400—still comes from there.
AUF: the acronym that allowed the barges to pass without paying
For over five centuries, marble arrived in Milan by water. It traveled down the Toce River, crossed Lake Maggiore, entered the Ticino River, and then the Naviglio Grande Canal, all the way to the Sant’Eustorgio dock.
From there, an ingenious solution was needed: the Conca di Viarenna, also known as the “Conca della Fabbrica” because it was built by the Cathedral’s own engineers. Thanks to its locks, the barges could reach the Laghetto, just a few hundred meters from the construction site. Filled in 1857, it is nowVia Laghetto, next to the state highway.
Every shipment bore the initials AUF, ad usum fabricae: no duties, no tolls. Perhaps that’s where the very Milanese expression “a ufo”—meaning “for free”—comes from. The last journey by water took place in 1920; then the trucks arrived.
Marmor from the Candoglia quarry: pink, durable, and difficult to extract
The quarry is located above Candoglia, a hamlet of Mergozzo, on the left bank of the Toce River, where the Ossola Valley begins. Lake Maggiore is just a few kilometers away, and Milan is about a hundred kilometers away.
There’s a catch, though. The vein is extremely narrow, so extracting the stone is difficult and expensive. The concession is free, but the work isn’t: the Fabbrica has been paying for the quarrymen, technology, and maintenance for six centuries.
Visiting the Candoglia quarry: a free tour date has already been set
Entry to the quarry is by guided tour only . The 2026 season has ended: visits were available on Saturday mornings, from June through mid-September, as part of a 90-minute paid tour.
In the meantime, you can get a close-up look at the marble of Milan’s Duomo on October 16. Then take a short walk to Via Laghetto: at the corner with Via Francesco Sforza, there’s still the open space where the barges used to dock.
