The Duomo and the Miracle of Bolsena
As it is usually narrated, Orvieto's Duomo was built in order to celebrate a fundamental event for the Christian world: the 1263 Miracle of Bolsena. As narrated by a sacred representation dating back to the first half of the fourteenth century and the subsequent popular tradition, a Bohemian priest, tormented by the doubt whether the consecrated host was Christ's body and blood, went on a pilgrimage to Rome in 1263 to strengthen his faith. On his way back he stopped in Bolsena to celebrate mass at the altar of Saint Christina's Basilica; at the moment of consecration he saw the broken host spill some stills of blood, that stained the Corporal, a linen cloth used during the functions. Once Pope Urban IV, who had been residing in Orvieto since 1262, learnt about the miracle, he sent the town's Bishop to Bolsena so that the latter would take the relic represented by the sacred linen cloth to the Church of Saint Mary; the Pontiff himself waited by the Rio Chiaro bridge for the relic to arrive and a solemn procession accompanied it to its final destination. The Orvietani thought the existing cathedral appeared too modest to host such a precious relic, therefore they decided a new religious building should be constructed, splendid and magnificent enough to match such a great miracle.
Besides this tradition, it is a proven fact that the old Church of Saint Mary Prisca was in such a bad condition that the most important ceremonies needed to be held in other places of worship; also, Pope Urban IV had issued the "Transiturus de hoc mundo" Papal Bull on 11 August 1264 which established and extended the Corpus Domini festivity to the whole Catholic world, with the underlying purpose to create a front against a multitude of heresies. Orvieto was experiencing a flourishing civil and economic development at the time, together with a great religious fever, to which the Miracle of Bolsena and the Transiturus Bull had certainly contributed. Therefore there was a general need for a new cathedral, and Francesco Monaldeschi, who served as Orvieto's Bishop between 1279 and 1295, took this responsibility upon himself: meeting a general wish, he envisaged the construction of an imposing and beautiful building, that required the demolition of the Church of Saint Mary and the Parish Church of Saint Constant.
In any case, even if legend more than real history, the traditional link between the Duomo and the Miracle of Bolsena has always been alive in the devotion of the locals; historians and scholars, such as Luigi Fumi, just to name one, have been aware of it too. Finally, Pope John Paul II, in the homily pronounced from Orvieto's Duomo on 17 June 1990, during the Corpus Domini celebrations, tried to clarify this matter, by stating: "even though the construction [of the Duomo] is neither directly connected to the solemnity of the Corpus Domini, established by Pope Urban IV in 1264 with the Transiturus Bull, nor to the miracle that had taken place in Bolsena the previous year, with no doubt the Eucharistic Mystery is here powerfully evoked by the Bolsena Corporal, for which the chapel that enshrines it now was purposely built".