A gesture of reverence in worship. It involves touching a knee briefly to the floor while holding the upper body upright, and then returning to a standing position. It is not required by the Prayer Book at any time. In some parishes it is a customary gesture of reverence for Christ's real presence in the consecrated eucharistic elements of bread and wine. Genuflections are often customary in parishes with an Anglo-catholic piety. Genuflections may be seen as people enter or leave a church, or the seating area of a church, or the vicinity of a tabernacle where the Blessed Sacrament is reserved. The celebrant and assisting ministers may genuflect at the end of the eucharistic prayer or after the words of institution concerning each element in the eucharistic prayer. Genuflection has also been associated with veneration of the cross at the Good Friday liturgy and with the affirming of the Incarnation in the Nicene Creed. The genuflection is from imperial and feudal ceremonial. The custom of genuflecting to the Blessed Sacrament dates from the eleventh century, and it was introduced into the Mass in the fourteenth century. Some prefer the profound bow as a more ancient gesture of reverence in worship.