The engineering marvel of the Pozzo di San Patrizio
The Pozzo di San Patrizio is an ancient well in Orvieto, Umbria, central Italy, built between 1527 and 1537 at the behest of Pope Clement VII who had taken refuge at Orvieto during the sack of Rome. The cylindrical well plunges down more than 50 metres in a double helix design, which enabled donkeys to carry empty and full water vessels in downward and upward directions without obstruction.
This amazing masterpiece of hydraulic engineering was originally named Pozzo della Rocca (‘Fortress Well’), as it is located close to Albornoz fortress, but was changed to Pozzo di San Patrizio (‘St Patrick’s Well’) in the 19 th century after monks in a nearby convent likened it to medieval legend of St Patrick’s purgatory.
After Rome was sacked in 1527 by renegade troops of the Holy Roman Empire under Charles V, Pope Clement VII fled to Orvieto where he took shelter in the city. Fearing that the city’s water supply would be insufficient in the event of a siege, the Pope commissioned Antonio Sangallo the Younger to build a large well that would ensure an abundant supply in case he should have to ride out another siege.
The architect-engineer Antonio da Sangallo the Younger set about constructing the well which he designed with a central shaft and two spiral ramps in a double helix, accessed by two doors, which allowed mules to carry water vessels down on one side and up on the other. His design was unique at the time; there were no other wells like it anywhere in Europe.
The cylindrical well measured 62 metres deep and 13 metres wide. Seventy-two windows provided illumination inside the well, and the steps are gently shelving, allowing them to be negotiated easily by the donkeys. There are 248 steps on each side of the well. At the bottom is a bridge that people could walk on to scoop up water.
Inside St Patrick’s Well. Photo source: BigStockPhotos
The Pozzo di San Patrizio is a work of skilled engineering that was preceded by hydrogeological research in order to identify the most suitable site to reach the clayey layer of the springs and tile part of the walls with bricks to improve their sealing properties. An inscription on the well says: ‘QUOD NATURA MUNIMENTO INVIDERAT INDUSTRIA ADIECIT’ (what nature stinted for provision, application has supplied).
As it turned out, before the well was completed, Pope Clement VII and Charles V reconciled their differences and the town was never besieged. However, the digging continued and in 1537, ten years after work first began, St Patrick’s Well was completed.