The famous well of San Patrizio is a structure built by Antonio da Sangallo the Younger between 1527 and 1537 on commission from Pope Clement VII. On the occasion of the sack of Rome, the pontiff took refuge in Orvieto and ordered the construction of a well that would serve as a water supply in case of siege of the city.

Initially it was to be used for the fortified fortress, that is why at the time of construction it was called "Well of the Rock". Later it was also called "Purgatory of Saint Patrick" and only in the nineteenth century took the current name of Pozzo di San Patrizio by the friars of the Convent of the Servants, who were known for the "legend of the Irish saint".

Patrizio would have been the keeper of a bottomless cave, the famous "Well of Saint Patrick" precisely, from which after seeing the pains of Hell you could access the Purgatory even to glimpse Paradise.

The project of Sangallo, who was already working on the fortifications of the city, was inspired by the spiral staircase of the Villa del Belvedere in the Vatican, thus creating a brilliant helical system of steps so that the ways to go down and up the path of the well (depth about 58 meters) did not meet each other generating "traffic" problems.

Today it is a real pleasure for the approximately 250 thousand annual visitors to descend to its depths along the 248 steps that make up it and touch this work of great architectural ingenuity.

Here are some curiosities:
- The well is 54 meters deep and was made by digging into the tuff of the plateau on which stands Orvieto
- Cylindrical with a circular base and a diameter of 13 m
- The steps to climb up or down are 248, while the windows that give light are 72
- The two stairways are connected by a bridge still practicable
- At the bottom of the well, the water level is kept constant thanks to a natural spring that supplies the cavity and an outlet that drains the excess water
- On the entrance of the well the inscription "quod natura munimento inviderat industria adiecit" ("what had not given nature, procured industry") celebrates human ingenuity as a skillful means able to overcome the deficiencies of nature