The Church only instituted the feast of the Holy Sacrament in the 13th century. During the first twelve centuries the Church was content to celebrate the anniversary of the institution of the Eucharist on the Thursday of Holy Week. But after some heretics dared to blaspheme against this Sacrament and raised doubts about the real presence of Jesus Christ under the Eucharistic species, the Church judged in favour of establishing a special festival in honour of the real presence on our altars of the Body and Blood of Jesus Christ. This festival was called the Feast of the Holy Sacrament; it was also called and is still called Corpus Christi, the festival of the Corpus or Body of Our Lord.

Now of whom did God did make use for the institution of this festival? A devout little girl called Julienne.

Born in 1193 in the village of Rétienne, near Liège, Julienne was orphaned at five years of age. She was then entrusted to the nuns of the convent of Cornillon, on the outskirts of a suburb of this city. There she distinguished herself by her application to study, work and the most sublime virtues of Christian perfection, and especially by an ardent love for the wonderful Sacrament of our altars. We can see that Julienne, who was the recipient of heavenly illumination, was preoccupied for a great many years by the idea that the Church lacked real clarity because its Divine Spouse did not have a special festival in honour of His Sacred Body and Priceless Blood. She spoke about this to Jean de Lausanne, a man of singular virtue and a canon of St Martin's church in Liège, who in his turn mentioned it to Jacques Pantaléon, an archdeacon, and several other people distinguished by their illumination and piety. They agreed unanimously that it was a good thing in oneself and very useful for the Church to celebrate the institution of the Eucharist with more pomp and magnificence that had hitherto been the case. In spite of this, Julienne was to suffer for a long time by seeing her intentions ignored and her views disputed: it is a characteristic of all major things that are done within the Church that they are established and strengthened amidst obstacles and contradictions. Lastly, after twenty years of argument, disputes and fruitless activity, a pious Bishop, Robert de Torotte, who had moved from the seat of Langres to that of Liège, brought her wishes to fruition. In 1246 he promulgated a decree throughout his entire diocese instituting the festival of Corpus Christi, which was fixed on the Thursday after Trinity, and forced himself to read the Office during the illness of which he was to die shortly after. The canons of the Collegiate Church of St Martin were the first to celebrate this moving occasion. But it was essential that it also be well received elsewhere.

Saint Julienne was even regarded as a visionary, and the feast-day as a useless novelty: it was argued that to honour the Holy Sacrament all that had to be done was to celebrate the Holy Sacrifice of the Mass each and every day; a special festival appeared to be superfluous. Accordingly while some openly rejected the new festival others expressed their reserve about it until the Universal Church had spoken. The latter finally did speak, and it was the former Archdeacon of Liège, Jacques Pantaléon - who had now become Pope under the name of Urban IV - who was now the head of it. On September 8 1264 he published a Bull extending the festival to all of Christendom, and charged St Thomas Aquinas, then a professor in Orvieto, with the task of composing the office for it. Urban IV died in the same year as he published the Bull of which we have just spoken. After his death the civil wars that then disturbed Italy caused the new festival to be forgotten and, except for the diocese of Liège, it was not celebrated anywhere. More than 50 years later Clement V, at the Council of Vienna, ordered the execution of the Bull of Urban IV and the festival then started to be generally celebrated. John XXII, successor of Clement V, ordered that Corpus Christi be celebrated with an Octave and that the Holy Sacrament should be carried in procession. Martin V ordered that the festival be celebrated to the sound of bells. Lastly, in 1433 Pope Eugene IV confirmed the Bull of Martin V, enriched the festival with many papal indulgences and required all the Bishops of Christendom to publish pastoral letters on this subject throughout their dioceses.