St Thomas of Canterbury 

The Feast of Corpus Christi, also known as the Solemnity of the Most Holy Body and Blood of Christ, celebrates institution of the Eucharist.

The Corpus Christi procession is a centuries-old tradition of the Catholic faith to process the Real Presence of Jesus — the Eucharist — in public. It was established in Liege, Belgium, in 1247. Pope Urban IV extended it to the universal Church almost two decades later, and the Corpus Christi procession followed soon after.

Saint Pope John Paul II, in his Apostolic Letter Mane nobiscum Domine he urged for the procession on Corpus Christi: "... let us also celebrate with particular devotion the Solemnity of Corpus Christi, with its traditional procession. Our faith in the God who took flesh
in order to become our companion along the way needs to be everywhere proclaimed, especially in our streets and homes, as an expression of our grateful love and as an inexhaustible source of blessings."