At the foot of the Candoglia village, in the municipality of Mergozzo, the Toce River and at the mouth of Val d'Ossola, there are the wellsprings of the Duomo, the quarries where the marble that composes the Milan Cathedral originates from.
Its mottled pink crystalline beauty, combined with exceptional resistance due to physico-chemical properties, represents one of the few cases in which the construction material used not only influenced the building, the architecture and the statics but also and above all the ornamental part.
It was Gian Galeazzo Visconti, the founder of Veneranda Fabbrica del Duomo, who decided to replace the brick, the material originally chosen for construction of the Duomo in the initial project, with marble, and to this end on 24th October 1387 he gave Veneranda Fabbrica exclusive use of the marble quarries of Candoglia. The privilege granted included not only the quarrying rights but also transport of the marble to Milan via the waterways.
Initially Veneranda Fabbrica used the “delle Piane” open quarry, located just above the river Toce, but subsequently decided to move the quarrying activity farther up, to an altitude of 580 m, due to landslips, landslides and lack of raw material.Iron tools, such as pickaxes, sledgehammers, spikes, wedges and crowbars, were the only technological equipment used in the quarries, and some of them are still used today. With the advent of electricity, towards the end of the 20th century, quarrying became more effective thanks to technological innovations (high speed diamond wire, diamond chain blades etc.), which made preparation of the marble blocks quicker and more selective.
The marble blocks were transported from Candoglia to Milan by means of the waterways from the river Toce to Lake Maggiore, along the Ticino and the Naviglio Grande canal and then into the city as far as the darsena [dock] of S. Eustorgio. Via the system of locks, created by Veneranda Fabbrica, the marble arrived at Laghetto, now Via Laghetto, only a few hundred metres from the Cathedral construction site.To enter the city, the boatmen used a password: “AUF”, the abbreviation of “Ad usum fabricae”, i.e. for the use of the Fabbrica, which exempted them from payment of the toll.The custom survives in Lombardy in the expression “A ufo” which means “free of charge”.
In 1874 the Main Quarry was connected to the village of Candoglia by a road to facilitate access of the personnel to the quarry and transport of the marble to the quay on the river Toce.
The narrow vein of this marble makes extraction difficult and costly. A further difficulty, both in past centuries and in modern times, is the percentage of marble that can be used out of the total amount quarried, which is between 10 and 25%.
All these unknown quantities, however, have never halted the momentum of Veneranda Fabbrica which tackled this huge undertaking by using, unsparingly, all its resources in terms of intellect and manpower, and worked enthusiastically but rationally towards its objective.