There are several elevations in the Latin Rite of Holy Mass, the two most notable being the regular elevation prior to Communion, which is accompanied by the words "Ecce Agnus Dei" ("Behold, the Lamb of God"), and the major elevation, which takes place immediately after the Consecration, at which the priest raises the Blessed Victim above his head for all to behold and adore. While the former elevation is quite ancient - it can be traced back at least to the time of the Apostolic Constitutions of the 4th century - the latter elevation is a relatively recent addition to Holy Mass, having begun sometime in the late 12th century and integrated into the official rubrics by Pope St. Pius V in the 16th century. It is this latter elevation which, in the Latin Rite, is generally known under the name "elevation." As such, the elevation is a prime example of authentic liturgical development.
It is worth noting that the development of the elevation as a standard part of the Holy Sacrifice of the Mass contributed greatly to the practices of Eucharistic processions and Eucharistic adoration - both of which have become part and parcel of traditional Catholic spirituality. Elevation itself is now understood as such a theologically significant moment during the Sacrificial Mystery - it is mystically symbolic of Our Blessed Lord being raised upon the cross at Calvary - that the Mass, whether in the Extraordinary Traditional Latin or the Ordinary vernacular form, is practically unthinkable without it. It is a supremely Catholic practice, as it is a powerful expression of our faith in and devotion towards the Real Presence of Our Blessed Lord in the Sacrificial Victim. And who among the faithful has not, at least once, felt the urge to call out, as did our forefathers in the Faith, "Hold, sir priest! Hold!" so that we may savor the moment?
Below you will find images recording the continuity of the practice of elevation throughout the last 800 years. In many of them, you will notice that the altar server is holding either a tall candle or a staff topped with a candle. This is the so-called "elevation candle," which was used to illumine the Sacred Victim in poorly lit churches and chapels, making it more easily visible to the faithful. In many traditional parishes today, the elevation candle, placed on the Epistle side of the altar, is lit immediately after the Sanctus and extinguished either after the sanctuary door is closed or after the final oblutions. At High Mass, this function can be taken over by torch-bearers, who kneel at the foot of the altar, similar to the depictions below.