A word from Fr. Mock about the Solemnity we celebrate today:
In 1246, Bishop Robert de Thorete of the Belgina diocese of Liège, at the suggestion of St. Juliana of Mont Cornillon (also in Belgium), convened a synod and instituted the celebration of the feast. From Liège, the celebration began to spread, and, on September 8, 1264, Pope Urban IV issued the papal bull "Transiturus," which established the Feast of Corpus Christi as a universal feast of the Church, to be celebrated on the Thursday following Trinity Sunday which was last Sunday.
At the request of Pope Urban IV, St. Thomas Aquinas composed the office (the official prayers of the Church) for the feast. This office is widely considered one of the most beautiful in the traditional Roman Breviary (the official prayer book of the Divine Office or Liturgy of the Hours), and it is the source of the famous Eucharistic hymns "Pange Lingua Gloriosi" and "Tantum Ergo Sacramentum." The Prayers the priest prays from the Chair and the Preface were written by Saint Thomas.
For centuries after the celebration was extended to the universal Church, the feast was also celebrated with a Eucharistic procession, in which the Sacred Host was carried throughout the town, accompanied by hymns and litanies. The faithful would venerate the Body of Christ as the procession passed by. In recent years, this practice has almost disappeared, though some parishes still hold a brief procession around the outside of the parish church.