While St. Juliana of Liege is regarded as one of the primary inspirations behind the feast of Corpus Christi, there was also a Eucharistic miracle that led to its universal celebration.
According to various accounts, one of the clergy who assisted St. Juliana during her life was eventually named Pope Urban IV. He was then living in Orvieto, Italy, when a priest from Bolsena approached him about a Eucharistic miracle.
The Eucharistic miracle of Bolsena
Author Heinrich Stieglitz narrates a popular account of the story in his book The Church Year: Talks to Children:
One of the priests who had lent [St. Juliana] aid was later raised to the high dignity of Pope and it rested with him to finish the task that Juliana had begun.
This also happened in a remarkable way. At that time there was a certain pious priest who was continually troubled by a doubt of the Real Presence of Jesus in the Blessed Sacrament. One day he had just consecrated at Holy Mass when blood began to trickle from the Sacred Host. In his fear he tried to hide it, but the drops left red stains upon the altar. The whole affair could not after that be concealed. Filled with remorse the priest hurried to the Holy Father and told him all.
Pop Urban IV investigated the incident and found it to be a miracle. It was enough to convince him that the feast of Corpus Christi, which had already been celebrated at a local level, needed to be spread throughout the entire Catholic Church.
It is believed that he "published an encyclical in which he commanded that the Thursday following Holy Trinity be observed throughout the whole world as the feast of Corpus Christi."
Pope Urban IV then commissioned St. Thomas Aquinas to write the famous hymns that are still sung on the feast of Corpus Christi and in other liturgies of the Church.
