The Feast of Corpus Christi (liturgically correct "Solemnity of the Body and Blood of Christ"), under whose patronage this chapel was placed, was introduced in 1164 by Pope Urban IV with a so-called "bull" as binding for the Roman Catholic Church. It states (among other things):
"We have therefore deemed it right and proper, in order to strengthen and exalt the true faith, to decree that, in addition to the daily commemoration which the Church makes of this holy sacrament, a special feast be celebrated every year on a certain day, namely, the fifth weekday after the Octave of Pentecost. On this day, the pious people will strive to hasten in great numbers to our churches, where hymns of praise will resound with holy joy from the clergy and laity. On this holy day, hymns of joy shall resound from the hearts of the faithful, from their mouths and from their lips. On this memorable day, faith shall triumph, hope shall rise, mercy shall shine, piety shall exult, our temples shall resound with songs of joy, and pure souls shall tremble with joy. On this day of devotion, may all the faithful hasten to our churches with joy of heart, and with unlimited obedience there relieve themselves of their duties and thus celebrate this great feast in a worthy manner. May it please God to inflame them with such holy zeal that, by practicing their piety, they may increase in merit with the One who redeemed them. May this God, who gives himself as their food, also be their reward in the other world."