The emergence of Corpus Christi as a Christian feast didn’t happen until the second half of the thirteenth century with the efforts of a nun called Juliana of Liège.
Since childhood, Juliana had been claiming that God had been telling her that there should be a feast day for the Eucharist and eventually she petitioned the Bishop of Liège. In those days bishops could order feasts in their local dioceses. The bishop agreed to the feast and convened a synod in 1246 and ordered that a celebration of Corpus Christi should be held annually.
The Corpus Christi celebration only started to become more widespread after both Juliana and the Bishop had died. In 1264 Pope Urban IV issued the papal bull Transiturus in which Corpus Christi was made a feast throughout the entire Latin Rite. He fixed it for Thursday after the “octave” of Pentecost when only designated celebrations or special feasts were blessed. This feast is celebrated on a Thursday in remembrance of the institution of the Eucharist (the last supper) which takes place on Maundy Thursday, the eve of Jesus’ death on the Cross.
Corpus Christi is primarily a Roman Catholic feast, but it is also acknowledged in the calendar of a few Anglican churches, most notably the Church of England. It is also celebrated by some Western Rite Orthodox Christians. Across many parts of medieval Europe, Corpus Christi was a popular time for the performance of mystery plays.
Along with Lent, Advent, Easter, Pentecost and Christmas, Roman Catholic Bishops have a duty to be present at their cathedrals on Corpus Christi.