In the 13th century a priest on pilgrimage to Rome was suffering doubts about the Eucharist. During a Mass his Host become flesh and bled upon the linen corporal. Hearing about this, Pope Urban IV desired that a feast of the Body and Blood of Christ should be celebrated everywhere to honour this Eucharistic miracle. St Thomas Aquinas (d 1274) composed the Mass and Office texts. Nowadays, the feast’s celebration is often transferred from its Thursday to the following Sunday. The Collect, assumed unchanged into all editions of the Missale Romanum, is magnificent: