The Pozzo di San Patrizio - A 62 meter well dug into the tufa rock completed in 1537 to supply protected water to the ancient hilltown. The circular well has two diametrically opposite entrances leading to two concentric spiral staircases that never cross. One for going down and one for returning after crossing the narrow walk at the bottom. Water was hauled up the 248 ramplike steps.
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Italia.it - Il Pozzo di San Patrizio a Orvieto, un capolavoro di ingegneria commissionato da Papa Clemente VII nel 1527 per garantire acqua alla città in ogni momento dell'anno, è profondo 62
File:Orvieto italy well.jpg - Wikipedia