Eucharistic Miracle of Bolsena.
In the summer of 1264, a Bohemian priest named Father Peter of Prague came to Italy to be received in audience by Pope Urban IV, who was residing at Orvieto that summer together with numerous cardinals and theologians, among whom St. Thomas Aquinas was also present. Father Peter of Prague, just after being received by the Pope, set out for his return trip to Bohemia.
Along the way, he stopped at Bolsena, where he decided to celebrate Mass in the church named in honor of St. Christina.
The priest began to celebrate Mass and had just finished pronouncing the words of consecration when he saw that the Host which he held in his hands had been transformed into living Flesh sprinkled with red Blood, which spilled onto the altar, staining the altar cloth and the corporal.
Thanks to this Miracle, the Lord strengthened the faith of the priest, who despite his manifest piety and moral uprightness, often nurtured doubts concerning the Real Presence of Christ under the species of the Bread and consecrated Wine.
News of the Miracle spread at once, so that both the Pope and St. Thomas Aquinas could immediately confirm the Miracle in person. After a thorough examination, Pope Urban IV approved the miracle. He then decided to extend the feast of Corpus Christi, which up to that time had only been a local feast of the Diocese of Liegi, to the entire Church universal. The Pope assigned St. Thomas the task of drawing up the liturgy which was to accompany the Papal Bull “Transiturus de hoc mundo ad Patrem”, in which the reasons for which the Eucharist is so mportant for the life of the Church were set out.
It is still possible today to venerate the Relics of the altar cloth and the corporal stained with Blood which are preserved in the Cathedral of Orvieto.