The hilltop town of Orvieto lies upon the boundaries of Tuscany, Umbria, and Lazio, near an important drainage divide of the River Tiber that flows to Rome and the River Arno that flows to Florence and Pisa.  It is an opportune site for examination of the influence of topography and bedrock geology on city planning, water resources, and life above the floodplains. The “hilltop” is a promontory formed by the erosion into an ignimbrite outflow sheet produced by a pyroclastic eruption from the Bolsano crater, immediately to the west.

View from the east side of the cliffs of Orvieto.

Gothic facade: bas reliefs recount biblical stories.

Alabaster window within the Duomo.

Rendering of the original stratigraphy and erosion to create the Orvieto promontory.

Pigeon coop within an alcove carved from the volcanic tuff.

St. Patrick’s Well – entrance.

Underground City

Huge numbers of caves run under Orvieto- more than 1200 have been identified. all are artificial, man-made, dug over 3,000 years. Began with 8^th century BCE Etruscan settlements at Orvieto.  Readily fortified but without a surface water source, the ancientn Orvieto needed water so the Etruscans dug deep shafts through the tuff layer down to a water source above the “aquitard” of marine clays, below.  They also created cisterns for rain water and connected the cisterns via a network of tunnels. Periodically Orvieto was attacked and destroyed by the Romans.

• next, caves dug from the 5^th century AD, barbarian tribes in the region, needed building materials
• most of the caves are private and under homes
• Orvieto sits on a block of tuffo and pozzolano (both volcanic), a clay layer rests below the volcanic layers
• 100,000 years ago a volcanic eruption covers regions with tuffo and pozzolano, the krater is now a lake
• most of the volcanic rock eroded away because they are porous and friable. This creates a great environment for springs to form
• inside we visit an olive oil mill that is set up in one of the many caves
  • was used until at least 1697, dates back to the 1300s
  • cave used because of consistent temperature which is 15C and 60F
  • Another cave area was a quarry for cement mortar.  We have a document from 1882 referencing a request to exploit the quarry; permission was granted 4 days later.
    • Whole quarry was dug in 3 months
    • Also visit an Etruscan well shaft that was turned into a dump when they did not find water.  In excavation, 6^th century BC rooftiles were found in it.
      • Shaft was 25 m deep when it ends.  Water was probably close to 80 m deep. How did they breathe?
      • Cave #6
        • was a pigeon coop
        • only needed water supply as pigeons are self-sufficient, bringing food home for their young
        • served as a “storage” area for food if the city was under siege. Pigeons are delicious, and are still considered a local delicacy.
        • 1632 passages for the pigeons in and out of the cave were closed by Pope Urban VIII.  Probably for reasons of tax evasion as the gates in/out of city were taxed and these passages were ways to slip in.
        • Conservation of underground caves
          • injections of pozzolano concrete into walls for stability
          • rain water problematic for erosion
          • Consolidation of the caves took place in a campaign from 1975-2000.  Further action will be taken in 2015, as the problem is ongoing.
          • Orvieto was a papal seat for various times, was a safe place for popes to take haven.  Caves are on average 10-15m below ground
          • The last room we visited continued the use of the caves as a safe haven—it functioned as a bomb shelter in WWII.  (It actually wasn’t safe for this use because of the inherent instability, but fortunately Orvieto was not bombed.)

Duomo de Orvieto

• laid first stone in 1290 (same time as Florence) and took 3 centuries to complete
• represents the moment of highest productivity, flourishing of Orvieto
• singular miracle in 1263 brought attention to Orvieto: the host bled on a linen cloth
• founded a celebration of Corpus Christi (June 8^th)
• comprehensive scheme designed for the façade
• ca. 1309- head of cathedral handed design over to Lorenzo Maitani, he changed the design to Gothic
• the façade is similar in style to Siena
• the roots of its style come from Norman France
• iconography typical of Middle Ages (stone sculpture)
• on the left is Genesis and Creation, middle is Hebrew prophets, and on the right the New Testament
• the overarching them is salvation and redemption
• we have excellent records from the construction process
• Mosaic program: Annunciation, Baptism of Christ, Apostles, father and mother of Mary, miracle of the Virgin birth. Mosaics originally date to 1354-1380 but portions have been restored over the years, leading to an intriguing mixture of styles that still contribute to a cohesive iconography.
• over the door- assumption of the Virgin, then the Virgin’s crowning at top
• sculpture: St. Michael, Lamb of God, and Gabriel
• figures around the Rose window: 12 Apostles, prophets, heads are doctors of the church
• Questions of typology: how do you build a new religion from an old one?
• texts of Hebrew Bible are predictions of Christian reality in the artistic programme
• art is NOT the Bible of the poor. Must take into consideration historical and ahistorical readings of art.
• We also should consider performative functions of the façade during processions, festivals or other activities.

Interior of the Duomo

• The Chapel of the Madonna di San Brizio (visited with the guidance of Mary Trull):
  • depicts the End of Days, Last Judgment, Antichrist, Christ Enthroned
  • described as epic, also very literary in theme (Virgil, Dante, Lucan, images from the Aeneid, Inferno, etc.)
  • unusual conglomeration of text, illusion and reality
  • Fra Angelico painted angels
  • Signorelli plays with illusion and reality
  • mixture of Classical and Christian themes on the wall
  • Natural: use of the term “earth” in the Vulgate.  God curses the “earth”
  • comparison of topography of hell (very mountainous) and heavenly scenes (no topography in heaven)
  • Dante uses rock symbolism in his works
  • chapel was begun in mid 15^th century (decorated by Fra Angelico).  He abandons the project in 1470s.  Signorelli takes over in the 1490s.
  • Scenes: Reign of the Antichrist
    • How do you visually differentiate the damned and the redeemed?  Redeemed often have beautiful bodies
    • scenes of natural catastrophe paralleling the apocalypse: sun/moon blotted out, reign of fire from heaven, mountains move
• images also from Dante’s Purgatorio
  • Virgil is depicted leading Dante
  • images from Canto 9, 10, 11
  • Purgatory is depicted as a mountain.  At the top of Mt. Purgatorio is Earthly Paradise
• description in Dante of 3 step of different stones:
  • White marble (self-reflection), grey stone (penance), red porphyry (redemption/blood of Christ)
• The decoration of the chapel makes tangible the very real stakes of the Eucharist.

Readings: Geology                                        (other resources are linked within the text, above)

• del Monaco et al., “Field Guide to Orvieto, Civita de Bagnioreggio, & Ancona,” 2nd World Landslide Forum, 2011, pp. 1-17.
• Morello N., “Steno, the Fossils, the Rocks, and the Calendar of the Earth,” in Vai GB et al., The Origins of Geology in Italy, GSA Special Paper 411, 2006, pp. 31-42.
• Cencetti, Corrado et al., The Rock of Orvieto (Umbria, Central Italy), Giornale di Geologia Applicata 1 (2005) 103–112

 Four-stage geological evolution of Orvieto.