At length, after a long silence, Pope Clement V., Bertrand de Got, took up the matter once more, and by his influence the Œcumenical Council, which he had assembled at Vienne in 1311, authorised the festival and enjoined its observance throughout Christendom. For this end, he renewed the constitution of Urban IV. in his own bull _Si Dominum_. Neither in this document, nor in the constitution of Urban, is there any mention of a procession of the Blessed Sacrament, but only of a Mass and the office. The procession was a later addition which, like the festival itself, gradually spread throughout different dioceses and countries. It was not, however, altogether a novelty, for already in the eleventh century, the Benedictines in England carried the Blessed Sacrament on Palm Sunday in procession outside the church.[278] The Corpus Christi procession, more recent than the introduction of the feast itself, was at first a much simpler affair than it is at present. As early as the twelfth century, it was by no means unusual to carry the Blessed Sacrament hidden from sight in a chalice or pyx round the church, and a procession of this kind is specially provided for in the ritual for Holy Week.[279] The _Ordinarium_ of the Church of Rouen contains directions for the performance of such a procession, but unfortunately the date of this document is uncertain.[280] According to this, the Blessed Sacrament was carried round the church by two priests in white chasubles, accompanied by four choristers carrying censers. Two other clerics carried torches, and the remainder, vested in copes, sung various versicles and responses. The shrine in which the Blessed Sacrament was carried was placed in the middle of the choir, and the Sacrament was censed by a priest accompanied by a deacon, while the singers remained kneeling. They sang, _Ave, verum corpus natum, etc._, which the choir repeated still kneeling, and then added other hymns. When this was concluded, the archbishop was to give the blessing and commence the Mass.