Pozzo di San Patrizio

The Pozzo di San Patrizio, or Well of St. Patrick, is a historic well in Orvieto, in the Umbria region of central Italy, a city built high on a flat volcanic butte fortified with defensive walls. It was constructed between 1527 and 1537 by the architect-engineer Antonio da Sangallo the Younger of Florence at the request of Pope Clement VII, who had taken refuge in Orvieto after the 1527 sack of Rome and feared the city's water supply would fail under a prolonged siege. Sangallo surrounded the central shaft with two separate helical ramps arranged as a double helix, so that donkeys carrying empty and full water vessels could descend and ascend without crossing paths. The well is 53.15 metres deep with a base diameter of 13 metres, and its two spiral ramps together hold 248 steps lit by 70 windows. Its name recalls medieval legends that St. Patrick's Purgatory in Ireland gave access down to Purgatory itself, a way of describing its extraordinary depth.