CORPUS CHRISTI, FEAST OF (Lat. _festum corporis Christi_, i.e. festival of the Body of Christ, Fr. _fête-Dieu_ or _fête du sacrement_, Ger. _Frohnleichnamsfest_), a festival of the Roman Catholic Church in honour of the Real Presence of Christ in the sacrament of the altar, observed on the first Thursday after Trinity Sunday. The doctrine of transubstantiation was defined by the Lateran Council in 1215, and shortly afterwards the elevation and adoration of the Host were formally enjoined. This naturally stimulated the popular devotion to the Blessed Sacrament, which had been already widespread before the definition of the dogma. The movement was especially strong in the diocese of Liége, and when Julienne, prioress of Mont-Cornillon near Liége (1222-1258), had a vision in which the need for the establishment of a festival in honour of the Sacrament was revealed to her, the matter was taken up with enthusiasm by the clergy, and in 1246 Robert de Torote, bishop of Liége, instituted such a festival for his diocese. The idea, however, did not spread until, in 1261, Jacob Pantaleon, archdeacon of Liége, ascended the papal throne as Urban IV. By a bull of 1264 Urban made the festival, hitherto practically confined to the diocese of Liége, obligatory on the whole Church,[1] and a new office for the festival was written by Thomas Aquinas himself. As yet the stress was laid on reverence for the Holy Sacrament as a whole; there is no mention in Urban's bull of the solemn procession and exposition of the Host for the adoration of the faithful, which are the main features of the festival as at present celebrated. Urban's bull was once more promulgated, at the council of Vienne in 1311, by Pope Clement V.; and the procession of the Host in connexion with the festival was instituted, if the accounts we possess are trustworthy, by Pope John XXII.
From this time onwards the festival increased in popularity and in splendour. It became in effect the principal feast of the Church, the procession of the Sacrament a gorgeous pageant, in which not only the members of the trade and craft gilds, with the magistrates of the cities, took part, but princes and sovereigns. It thus became in a high degree symbolical of the exaltation of the sacerdotal power.[2] In the 15th century the custom became almost universal of following the procession with the performance of miracle-plays and mysteries, generally arranged and acted by members of the gilds who had formed part of the pageant.