Blessed Juliana of Cornillon, who lived in 13th century Belgium, had a vision in which she saw a full moon darkened in one spot. She heard a mysterious, heavenly voice state that the moon represented the Church at that time, and the dark spot showed that a great feast in honor of Corpus Christi was missing from the liturgical calendar. She reported this vision to the local ecclesiastical authority, the Archdeacon of Liège, Jacques Panteléon, who was later to
become Pope Urban IV.
In 1246, the Bishop of Liège, Roberto of Thourotte, established within his diocese a feast in honor of the Holy Sacrament, and it was celebrated for the first time on June 5, 1249. In 1264, Pope Urban IV (the former Archdeacon of Liège, to whom Blessed Juliana reported her vision) issued a papal bull extending the celebration to the universal Church.
He also commissioned St. Thomas Aquinas to compose the Office for the Mass and Liturgy of the Hours for the feast.