The feast of Corpus Christi, now known as Sacrament Sunday, originated in the thirteenth century, in 1246, in the diocese of Liège. During this celebration, the host is carried around in a solemn procession. In the beginning, the host was kept in a puxis, a closed box on a stand. When the visual aspect became more important, the host was displayed in a specially designed shrine. This gave rise to the Latin name ostensorium or monstrance. The first monstrances took the form of the monument above Christ's tomb in Jerusalem. As a result, they had the shape of a tower or cylinder, as in Jerusalem. Recent research shows that this monument dates back to the time of Emperor Constantine, around the year 345. In the nineteenth century, this tower shape was revived, as can be seen in the tabards of the Chapel of the Venerable. In this specific case, however, it is a radiant monstrance, in which the host is surrounded by rays, symbolising the divine Light. Because the host represents the real presence of Christ, monstrances are made from the most precious and refined materials, such as silver, gold, crystal and (semi-)precious stones. On high days, such as Maundy Thursday and Corpus Christi Sunday, the monstrance is carried in procession to the Chapel of the Venerable. After a short adoration and blessing, the ceremony concludes with the Tantum Ergo, a hymn in honour of the Blessed Sacrament, written by Thomas Aquinas.
