In 1263 a German priest, Peter of Prague, stopped at Bolsena while on a pilgrimage to Rome. He is described as being a pious priest, but one who found it difficult to believe that Christ was actually present in the consecrated Host. While celebrating Holy Mass above the tomb of St. Christina (located in the church named for this martyr), he had barely spoken the words of Consecration when blood started to seep from the consecrated Host and trickle over his hands onto the altar and the corporal.

The priest was immediately confused. At first he attempted to hide the blood, but then he interrupted the Mass and asked to be taken to the neighboring city of Orvieto, the city where Pope Ur ban IV was then residing.

The Pope listened to the priest's account and absolved him. He then sent emissaries for an immediate investigation. When all the facts were ascertained, he ordered the Bishop of the diocese to bring to Orvieto the Host and the linen cloth bearing the stains of blood. With archbishops, cardinals and other Church dignitaries in attendance, the Pope met the procession and, amid great pomp, had the relics placed in the cathedral. The linen corporal bearing the spots of blood is still reverently enshrined and exhibited in the Cathedral of Orvieto.

It is said that Pope Urban IV was prompted by this miracle to commission St. Thomas Aquinas to compose the Proper for a Mass and an Office honoring the Holy Eucharist as the Body of Christ. One year after the miracle, in August of 1264, Pope Urban IV introduced the saint's composition, and by means of a papal bull instituted the feast of Corpus Christi.

After visiting the Cathedral of Orvieto, many pilgrims and tourists journey to St. Christina's Church in Bolsena to see for themselves the place where the miracle occurred. From the north aisle of the church one can enter the Chapel of the Miracle, where the stains on the paved floor are said to have been made by the blood from the miraculous Host. The altar of the miracle, which is surmounted by a 9th- century canopy, is now situated in the grotto of St. Christina. A reclining statue of the saint is nearby.

In August of 1964, on the 700th anniversary of the institution of the feast of Corpus Christi, Pope Paul VI celebrated Holy Mass at the altar where the holy corporal is kept in its golden shrine in the Cathedral of Orvieto. (His Holiness had journeyed to Orvieto by helicopter; he was the first pope in history to use such a means of transportation).

Twelve years later, the same pontiff visited Bolsena and spoke from there via television to the 41st International Eucharistic Congress, then concluding its activities in Philadelphia. During his address Pope Paul Vl spoke of the Eucharist as being ". . . a mystery great and inexhaustible."